How to Build a Large Shed: Design, Materials & Permits Explained

Most property owners underestimate how much a large shed project involves before a single post goes in. Sizing, design, materials, permits, and construction all require decisions that affect the final result for decades.

Getting those decisions right from the start saves time, money, and the frustration of a structure that does not perform as needed.

Key Takeaways

• A building permit is required for most sheds over 10 square metres in Victoria, and skipping this step can prevent the structure from being insured or sold as an approved improvement.
• Rectangular Hollow Section (RHS) structural steel frames span wider clear distances than C-section, with universal beams or Open Web Trusses used for the very largest spans.
• Victoria’s Building Act 1993 classifies sheds as Class 10a structures, and council planning approval requirements vary by zone, setback, and Bushfire Attack Level (BAL) rating.
• A registered builder manages permits, fabrication, concreting, and construction as a single scope, removing the need for the owner to coordinate multiple contractors.

What Counts as a Large Shed, and What Will You Use It For?

A large shed typically starts at around 10 metres by 9 metres and grows from there. Farm sheds, machinery sheds, horse stables, commercial workshops, and hay storage all fall into this category.

The intended use shapes every other decision. A hay shed needs wide clear spans and good ventilation. A horse stable needs internal divisions and appropriate headroom. A machinery shed needs high eave heights and large roller door openings. Defining the use case first keeps the design process focused.

Sizing and Layout: Getting the Dimensions Right

Clear span width, wall height, and bay spacing all follow from the intended use. A machinery shed that needs to house large headers or grain equipment may require eave heights of 5 to 6 metres or more. A hay shed can typically work with lower sidewalls and wider bays.

Bay spacing affects how load is distributed across the frame. Wider bays reduce the number of internal columns, which is important for vehicle movement and storage access. Getting these dimensions right early avoids costly changes during fabrication.

Roof Style and Access Points

Gable roofs suit large sheds where internal height and airflow matter, particularly for equine and agricultural structures. Skillion roofs work well for lean-to additions or where a lower-profile structure is preferred.

Roller door sizing should match the largest piece of equipment or vehicle that needs to enter. A door that is 300 millimetres too narrow creates an ongoing operational problem. Specify door openings before finalising the frame design, not after.

Materials: Why the Frame Matters Most

The structural frame is the most consequential materials decision in a large shed build. It determines span capability, load capacity, and how long the structure performs without structural movement or maintenance issues.

Trusteel builds most large sheds using Rectangular Hollow Section (RHS) structural steel, which handles standard clear spans without intermediate posts. This matters for machinery access and open storage layouts. RHS is stronger under lateral and vertical load than C-section and performs better over a 30-plus-year lifespan.

Beyond that span, or where the shed carries genuinely heavy-duty loads, such as a wide-bay commercial workshop or a large-span machinery shed, Trusteel specifies universal beams (UB) for the portal frame and Open Web Trusses (OWT) for the roof structure instead. Both carry load across a wider bay than RHS alone.

C-section framing is the standard in most volume kit sheds. It is lighter and cheaper to produce. For light-duty storage where spans are modest and loads are low, C-section may be adequate. For commercial, agricultural, and equine applications where the structure needs to perform under real working conditions, C-section is a compromise that becomes visible over time.

RHS, UB, and OWT frames all cost more than C-section. The investment is in structural performance, longer spans without columns, and a shed that does not flex or degrade under load.

Steel is not the only option. Timber, or lumber-framed sheds, suits some applications, but steel outperforms timber in durability, pest resistance, and fire performance across most Victorian climates and rural settings.

Cladding and Roof Sheeting

COLORBOND steel is the standard cladding and roof sheeting choice for large sheds in Australia. It is durable, low-maintenance, and available in profiles suited to both wall siding and roofing.

Cladding choice affects thermal performance and condensation management. In large commercial or agricultural structures, condensation on the underside of roof sheeting can damage stored goods or create animal welfare issues. Insulation or anti-condensation blanket under the roof sheeting addresses this in most applications.

Permits for Large Sheds in Victoria: What You Actually Need to Know

Large sheds are classified as Class 10a structures under the National Construction Code. In Victoria, a building permit is required for most sheds above 10 square metres, as set out under Victoria’s Building Act 1993.

Setback distances from property boundaries and easements are governed by your local council’s planning scheme. These vary by zone. Some rural and farming zones have different thresholds or specific exemptions. BAL ratings in designated bushfire-prone areas affect what materials are required for the shed floor, walls, and roof.

When a permit is not obtained, the consequences are significant. The structure cannot be insured as a permanent improvement. It cannot be listed as an approved structure in a property sale. Councils can require its removal.

A registered Victorian Building Authority (VBA) builder like Trusteel manages the permit application on the owner’s behalf. That means no need to engage a private building surveyor separately or coordinate lodgement yourself. Under the Domestic Building Contracts Act, large sheds almost always exceed the threshold that requires a registered building practitioner. Owner-builder registration for a structure of this scale is rarely available or appropriate.

How Much Does It Cost to Build a Large Shed?

Cost depends on size, frame type, cladding, site conditions, and whether concreting is included. A structural steel-framed large shed, whether RHS, UB, or OWT, costs more than a C-section kit shed of equivalent footprint.

The offset is longevity and performance. A shed that flexes under load, requires maintenance within five years, or underperforms structurally creates costs that exceed the initial saving.

Trusteel’s quote covers design, permits, fabrication, and construction. The figure the customer receives is the full project cost, not a starting point that requires separate budgeting for a builder, concreter, and permit agent. 

To get a site-specific figure that covers the full scope, get a quote for your large shed.

DIY, Kit Shed, or Custom Builder: Which Suits a Large Shed?

A DIY large shed build is rarely appropriate in Victoria. Large structures require engineering certification, building permits, and concrete work that most owner-builders are not licensed to perform.

A kit shed from a volume supplier is a self-erect product. The owner takes on site management, permit coordination, and concreting as separate responsibilities. For a straightforward rural structure in a zone with simpler permit requirements, this can work.

A custom builder manages design, permits, fabrication, and construction as a single scope. For large structures with complex site conditions, BAL requirements, or commercial use, this removes the most common source of project cost blowout and delay.

How Trusteel Manages the Full Build Process

Every large shed Trusteel builds is designed from scratch to the site, the use case, and the equipment or operations it needs to support. The process runs in two stages.

Design and Engineering to Exact Requirements

Trusteel designs each shed to the exact dimensions and use requirements the customer specifies. There are no standard sizes forced on a project that needs something different. Frame specifications, bay spacing, door openings, and eave heights are all set to the actual use case.

Permits, Fabrication, and Construction as One Scope

Trusteel holds VBA registration and manages the permit process from application through to approval. Fabrication happens in-house. Construction and concreting are managed by Trusteel’s own teams.

Essentially, we manage the full scope under one contract, from first design conversation through to a completed, permitted structure. To understand what that looks like for your property, get in touch with Trusteel.

Frequently Asked Questions

What is the largest shed I can build in Victoria without a council permit?

In Victoria, a building permit is required for most sheds over 10 square metres. Planning approval from your local council may also be required depending on your zone and the shed’s size, siting, and use. Some rural zones have different thresholds. Check with your local council before assuming any exemption applies.

Do I need a registered builder to build a large shed, or can I act as owner-builder?

Large sheds in Victoria almost always exceed the threshold under the Domestic Building Contracts Act that requires a registered building practitioner. Owner-builder registration is generally not available for structures of this scale. A registered VBA builder manages the permit process and takes on the legal responsibility for the build.

Is it cheaper to buy a shed kit or have a large shed custom-built?

A kit shed has a lower upfront cost because it uses lighter C-section framing and transfers site management, permits, and concreting to the buyer. A custom-built shed with RHS, UB, or OWT framing costs more upfront and includes those services. For large structures where structural performance matters, the total cost of a kit shed is often higher once those additional scopes are priced separately.

How much does it cost to build a large shed in Australia?

Cost varies depending on size, frame type, cladding, site conditions, and whether concreting is included. RHS, UB, and OWT-framed sheds are priced higher than C-section kit sheds of comparable size. Trusteel provides a quote that covers the full project scope, so the figure reflects design, permits, fabrication, and construction rather than materials alone.

What is the difference between RHS, UB, OWT, and C-section framing, and why does it matter for a large shed?

RHS, universal beams, and Open Web Trusses are all structural steel that handles longer clear spans and heavier loads than C-section. Trusteel uses RHS as standard and moves to universal beams or Open Web Trusses for wider spans. C-section is an open-profile, lighter-gauge steel adequate for small light-duty storage, but not for large agricultural, equine, or commercial structures.