limestone basement walls

Has anyone used a PTAC unit(the units you see in motels) to heat/cool a basement? We were thinking this would be the way to go for ours. Our current system would be at it's limit if we added the basement to the system. Since the basement stays at a pretty constant temp most of the time (2 sides are underground) and the basement will be used mostly by my hubby for his office we really think a system that could be run when needed is the way to go. Just checking to see if anyone has had experience-good or bad with these things, Thanks, Annette P.S. PTAC stands for "packaged terminal air conditioning"

My husband and I would like to make our basement over into an apartment for my mother. The bewildering question seems to be ~ where do I start! We are prepared to do a lot of the work ourselves. There is a half bath and laundry facilities...we want to add a shower and a kitchen.