RV Garage Construction - Any Tips?

OP can you post a picture of that side of the house? Bigger door and 50' long as RVs have a way of growing. I used a swinging door...better insulation and no lost head room.

Do a Google search for RV homes for sale at TGO in Florida for ideas.

6" slab with rigid foam insulation underneath.
Don't know what you have for fuel so you may want to think of electric heating with the wiring in the slab.
Wall mounted AC units for Summer.
Frame construction with spray foam insulation. Painted drywall for sidewalls. Exterior to match existing house.
Truss roof frame with steel roof that snow will slide off of.
50 amp service and LED lighting.
14 x 14 roll up door with a 3 x 7 man door as well.
Level floor with a 1" lip at the door to prevent rain from blowing in.
Possibly connect to sewer or septic tank for waste disposal.
Fresh water available to fill tanks.
120 volt outlets around sidewalls.

Great suggestions above.

As big as you can make it. Room to work all around the coach, even put out pop-outs if possible. 14x14 door. Lights on the walls too are very helpful. I'd look into a heated floor as an option. While under construction, you may want to consider putting in a sewer dump just outside of the storage. Also consider installing an electrical connection both inside and out. I find that sometimes I prefer to work on things, polish, etc in the light of day.

The service pit is a great idea, although I'd hate to open up another side of the coach for me to obsess over!

I store my coach in a metal shed with a roll up door on the family farm about 20 miles from my house, which works ok, but has also given me the opportunity to think about the things I would change, and things I would do if I were building from scratch. In my case I have half of a 40x60 shed with a partition wall down the middle leaving me with a 40 ft long by 30 ft wide area, with a 12x12 roll up door offset to one side leaving me with about 5 more feet on the drivers side than on the passenger side. (my coach is 11'5" tall)

Here are a list of things I would do different, and things I may retrofit.

1, put lights on the side walls vs the florescent fixtures on the ceiling, as I don't care how well lit the roof of the coach is, instead I generally want to see stuff on the sides, and under the hood.

2, longer is better, I have a 29 ft long coach in a 40 ft long space, and would not want anything much shorter to allow full walk around with the roll up door closed, I would say plan on at least 2-3 ft front and back minimum clearance on the largest coach you might consider buying.

3, a 12 ft wide doorway can feel very narrow when pulling in after a long drive, particularly in the dark. On my coach a 12 ft wide roll up door gives me just over 11 inches on each side if perfectly centered, I have came very close to taking a mirror off in the dark before.

4, at least a partial service pit would be nice it does not have to be full standing height, something that would allow sitting height on a stool would go a long way, even something on the order of a 3x6 ft 3-4 ft deep service pit would be way better than inching around on ones back, though 4x8 would be nicer.

5, a higher roof to allow for rooftop RV maintenance indoors, I have a 13 ft ceiling height which is only about 18 inches of clearance over the top of the air conditioner shroud, which means less than sitting headroom clearance working roof top on a 10+ ft tall coach, even 6-12 more inches would mean a lot. Though in my case there is a second larger shed on the farm that I can use temporarily for such tasks.

6, As to the insulation, heating, etc. I can't help you there, I live in Louisiana where the temperature rarely gets below 20-25F (we did hit 18F this week though). In my case even with 18F lows, the shed my coach is in stayed above freezing with just the lights turned on and a couple of small electric heaters running on low (one in the coach, and one in the wet bay).

p.s. on the outlet just get a 50 amp and use a 50 to 30 pigtail adapter if you currently have a 30 amp coach. I have no drain, and a smooth level floor which can be an issue with heavy rain blowing in under the roll up door which can get slippery. The smooth floor is nice when working under the coach though vs more shall we say textured concrete finishes.

The biggest you can afford and zoning will allow. 12x14high door if it’s roll up. Personally I would have skylights rather than Windows to help keep people out. I’m jealous..