Steel RV Storage Building Sizes That Actually Fit

I have walked two jobs where the owner could not get the coach into the building we had just finished. Both times the roof height was right, the door was right, and the slab was poured thick enough. Both times the rig stopped six feet short of the opening because there was nowhere left to swing the front end around. One of those owners ended up paying for another 1,100 dollars of gravel and losing a row of young maples.

So before the dimensions, understand what you are really buying with an RV storage building. You are buying a path, a volume and a floor, and the path is the part people price last. Here is how I size one when the owner asks me on the gravel instead of over email.

Start with the rig, measured yourself

Do not trust the brochure height. Air conditioner shrouds, satellite domes and roof racks are not always in the published figure, and a coach that has been re-leveled on new springs can sit an inch or two higher than it left the factory. Park on level ground, run a tape up from the concrete to the tallest thing on the roof, and write that number on the back of your hand.

For reference, the rigs I measure most often land in these ranges. Class A diesel pushers run 12 ft 6 in to 13 ft 6 in tall and 34 to 45 ft long. Fifth wheels are usually 13 ft to 13 ft 6 in with the pin box, and 32 to 42 ft. Travel trailers are shorter, around 10 to 11 ft, and many of them are under 30 ft. A bass boat on a trailer is low, but put a tower on it and you are back to 11 ft 6 in with the trailer jack wound down.

The three dimensions, in the order that matters

Height first, then width, then length. That order surprises buyers who think of a building as a footprint.

The eave number is the one buyers argue with me about. A roll up door does not stop at the top of its opening. The drum and brackets want 18 to 24 inches of clear wall above the header, and the header itself eats several inches of frame. Order a 14 foot door into a 14 foot eave and your installer will call you from the site. Fourteen foot door, sixteen foot eave, every time.

Width is where people save money and then regret it. A 40 foot coach is 8 ft 6 in wide at the body and closer to 10 ft across the mirrors. Sixteen feet of inside width gives you three feet of elbow room per side, which sounds fine until you are backing in at dusk. Twenty feet lets you open a slide for a wash down and still walk past. If you plan to run one slide out for storage with a dehumidifier inside, you need that width.

Length should add six to ten feet beyond the rig. You want room for the ladder, a shelf wall at the back, and the hose reel that always ends up somewhere it should not be.

The apron nobody prices

This is the part I keep coming back to. Common advice online is all about roof height, and height is easy. The dimension that decides whether the building works is the clear, flat distance in front of the door.

A 40 foot coach needs roughly 45 to 55 feet of straight approach to line up and back in without a three point turn. Less than that and you are cutting the wheel hard while moving, which is how people hit the door jamb. I ask every owner to stand at the proposed door line and look straight out. If there is a fence, a septic lid, a well head or a mature tree inside 50 feet, we move the building or we turn it.

Pour the apron at least 20 feet deep in front of the opening, same thickness as the slab, with a slight fall away from the door. Gravel will do if the budget is tight, but it will rut where the drive tires load up, and you will be grading it every spring.

Slab, because an RV is not a car

A loaded Class A can weigh 30,000 to 36,000 pounds on two axles. That is three to four times a pickup, concentrated on a handful of tire patches.

I specify 6 inches of concrete at 4,000 psi with number 4 rebar on an 18 inch grid for anything over 20,000 pounds, over 4 inches of compacted clean stone. Fiber mesh alone is fine for a travel trailer building and not fine for a diesel pusher. Budget 9 to 13 dollars per square foot poured in most of the country in 2026, which on a 20 by 50 building with its apron is a real number, often 12,000 to 16,000 dollars.

One detail that costs nothing: ask for a broom finish rather than a smooth trowel. A smooth slab with a wet tire and a slight grade is genuinely dangerous, and I have watched a trailer slide sideways on one.

Keep the moisture off the roof of the rig

An uninsulated steel roof over a cold slab makes water. Warm air meets a cold panel, the panel sweats, and it drips onto a 90,000 dollar fiberglass roof all winter. Then owners blame the kit.

The fix is ordinary. Put faced insulation or a vapor barrier blanket under the roof sheets, run a continuous ridge vent with matching eave intake, and leave the slab to breathe. Two round turbine vents on a 50 foot building do not move enough air. If you are closing the building up tight for other reasons, a small dehumidifier on a humidistat costs less than one roof repair.

While the walls are open, run power properly. A 50 amp outlet for shore power, two or three 20 amp circuits for tools and a charger, and LED strips rated for the eave height. Doing it at erection time rather than later is the single cheapest upgrade on these jobs. If the door spec is still open, our breakdown of roll-up door cost by size and type shows what each extra foot of opening adds.

Before you sign

Three things to settle this week. Measure your rig yourself, including the ugliest thing bolted to the roof. Walk the approach with a tape and prove you have 50 feet of clear run at the door. Then check your covenants, because tall accessory buildings are exactly what boards object to, and our guide on steel building HOA approval covers the packet that gets a yes. More buildings people put up for a specific job are in the use cases section.

FAQ

How tall does an RV garage door need to be?

Measure your tallest roof fixture and add 12 to 18 inches. For most Class A coaches that lands on a 14 foot door, and for fifth wheels a 14 foot door is usually comfortable. Travel trailers often fit a 12 foot door with room spare.

What size steel building fits a 40 foot motorhome?

Twenty feet wide by 50 feet long with a 16 to 18 foot eave is the size I build most often for a 40 footer. That leaves room to walk both sides, store a ladder and a workbench at the back, and open a door without touching a wall.

Can I store an RV on gravel instead of concrete?

You can, and plenty of people do for seasonal storage. Expect ruts where the drive axle sits, tire sidewall damage from stones, and more moisture coming up under the rig. If the coach is parked for more than a few months at a time, concrete pays for itself in tire life.

Do I need a permit for an RV storage building?

Almost always, because of the height and the footprint. Anything with an eave above about 15 feet tends to trigger extra review on wind load, and some counties treat it as a separate accessory structure with its own setback rules. Ask before you order steel, not after.