I apologize if this type of thing has been addressed several times already.
I've got a 1 car garage, roughly 20' long by 10' wide. It has cinder block walls, and wood roof structure with galvanized roofing. The slab that it is on has some cracks, but our inspector said they weren't a problem. The whole structure is between 40 and 60 years old.
Our yard is thin, but long. The garage is almost on the property line, and has a couple feet on its corner that are eclipsed by the house. We don't want to sacrifice our yard by cutting it in half with a 2 car side-by-side structure.
So, what order should things be looked at? Extend the current cinder block garage another 20 feet with cinder block? Raze the garage and have a turnkey of some sort put up? What kind of person would be able to tell me if the garage is suitable to be extended/modified, or whether it should be torn down and rebuilt from scratch? If possible, I'm also looking at cost- extend with cinder block or wood? Would an extension be 1/2 or more of the cost of a demolished/rebuilt garage from the ground up? Or, would it be better to add onto the house? Is there one person that can answer these questions?

<-Blue line is property line, blue behind garage is possible expansion.