Best solution is for you to immerse yourself into all the issues of
. . . . "Can't Do That" . . .
that you seen to be getting from vendors you've talked with . . these include:
a) Setbacks (distance from property line that building must be)
b) Square feet restrictions (ie county or city rules about size of garage)
c) Height restriction
d) Utilities on your property (ie gas lines, buried electric, septic systems, etc)
This thread might go for many posts so will be better for you to . . .
. . . . Update GJ Profile . . . .
with your State and City so you will get best replies. Good luck.