There are many kinds of inspections - contractor inspections, pest inspections, foundation inspections, structural engineering inspections, and as Danielle pointed out you can get an inspection to give you an idea of how much it will cost to condo convert.
Remodeling unwarranted space can be tricky as it can trigger fines and fees that make it not worthwhile, although usually if you are not the one who did the unwarranted work they won't fine you. If you do things in a building that trigger an inspection, there is always the possibility that you will be required to remove/dismantle what has been done, so you want to be very careful.
We recently bought a 2 unit building with an unwarranted studio apt with a tenant in it. In order to condo convert we had to do what's called a demolition eviction, which removes that unit from the rental market permanently. In the end it depends on the specifics of the building and the work done, so make sure you have a representative that knows the ins and outs of these kinds of buildings, and make sure you talk to an attorney who specializes in this area BEFORE you do anything.
Lance King/Managing Broker