Hey Mark,
I converted our 1 carport space into the Lone Star Arcade as we do not have a garage either which took less than 6 months to build. A shed as someone proposed pre built or not could be a solution in your yard. Even if it was small space where you could set up a couple machines at a time but still have room to restore machines and sell them may be the way to go. I had someone build us a 10 x 16 shed in our yard for $3000.00
Just my 2 cents.
Ken