Been wanting to build a garage in the back yard for years. I was able to secure a variance from the local township (I'll spare the details) for a maximum of 950 sq ft, they will not allow anything bigger. Essentially 26 x 36' 6". Big enough for four cars, two deep plus some working room. I have a few questions as I work with the architect getting the plans together.
1. Floor thickness 4" or 6"? Future plans may include the addition of a four post lift.
4" is fine for a four post lift. Plan out where you'll probably put it, and make sure the floor is flat in that area.
2. Overhead door width, two 10' or one 18' wide? The two 10' doors may prohibit me from parking the cars close side to side to maximize the working room along one side.
From the PDF you provided, I'd be hesitant to use two doors unless you like the look. I'd do it like you have illustrated, with one big door. I have a 18' x 8' door on my "attached" garage and wouldn't have it any other way. Some days you may want to park in the center of the garage, or back in something on a trailer, etc. and it's nice to have a big, wide doorway. One door opener instead of two is a bonus as well. Do yourself a favor though and make sure it's at least 8 feet high if you currently own or ever plan to own a full size pickup. Also make sure its insulated so you don't have to go back and add insulation later (another lesson I had to learn the hard way).
3. There will be a 2ft wall around the perimeter. Block or poured concrete?
I don't understand if you mean a stem wall for the actual garage or a second, outer wall holding back the yard. If it's just holding back the yard you'll want to compare costs on block vs poured and decide which you'd prefer to look at every day. 2 feet isn't very tall, so structurally either one is not that big of a deal. If you mean a 2 ft stem wall on the building I'd go poured concrete unless costs are prohibitive. I'd do (actually I DID do) a proper foundation with poured concrete stem wall for the building.
4. the interior height will be 10' 6" and will have "attic" trusses spaced 24" so I have some storage space.
As others have said, you may want to rethink this and go higher if possible if you're going to have a lift of any kind. I assume your trusses will span across the 26 foot garage distance. You didn't say what the pitch of your roof will be. I just built my new garage with 28' spans and a 4/12 roof pitch. I thought about attic trusses but realistically there would only be a few feet of room up there with my relatively shallow roof. Attic trusses will likely increase the truss costs as well over standard trusses, and you'll have to devise some way of getting up there while carrying whatever you plan to store. Stairs are best but take up room down below. I opted to skip it and get rid of stuff rather than store it.
5. Eventually interior will be insulated and sheet rocked
Good plan. Electrified too I assume.
6. Contemplating radiant floor heat - comments / experiences?
I considered it to the point of "analysis paralysis" and finally decided not to put it in. Depends on how much you plan to be out there in the winter months. I currently use a 5000 watt electric heater in my attached garage, and it actually works very well for the times that I'm out there working in the winter and really doesn't cost that much to run since it isn't on all the time. The new garage will probably get a gas fired heater, but I haven't got that far yet.
Thanks in advance,
Tom