Sounds similar to my shed set up only I don't have a sofa in there (yet)!!
When I say shed, its not your usual one that can only fit a lawn mower and a spade. It was custom built by the previous home owners and is almost as wide a my house and quite long plus it has its own electricity supply with a fuse box and everything so I have lighting and a heater.
I purposefully set it up so I could rescue a feral family living in the carpark area of a toby carvery and hotel. Once I have sorted this family I hope to help more, possibly by fostering for CP or another local rescue
Good luck...I'm sure your garage won't stay empty for long