To build....
I know you can't change your gaurage,,,,
You need a 12'x24' space to be comfortable building. ...more wide to fit the wings, You can build in less. I have done it in 10x 20, more than once.
Get make it 12 x 26 if you can ...
I use a 20x20 now and it is not right. too wide and too short...but its built 28 RVs....