Actually common here is 2x4 and 16 or 24" o.c. So I can go either way for about the same money.
I am in Arkansas and my shop is 2x4 walls and truss roof.
Not "Formula" but I have a 1982 Mecham Racing Motor Sports Edition Trans AM with the motor out right now 70,000 original miles, 1 of 9 that are red.
And the first project in the new shop will be my 1983 25th anniversary Daytona 500 Trans Am hardtop 1 of 116 built that we will restore for my son. first 2 pics in hardtop section bottom of page here...
http://www.transamaction.de/pace-cars-english.html
No doubt, the word of mouth has spread about my wrenching and I have outgrown the little project shed.
Hey bro!

I find it's a good way to make extra ca$h and nobody around here wants to do watercraft or performance trans builds. I feel like I'm pretty close to going full time on my own.