Thinking of an addition

I have a 105 yrs old home here in Barrie that has a useless sunroom addition on the back that I'd like to take down and replace with something more usable.

Overall dimensions would be 20x24, single story, with a poured foundation (want a basement with a 8' ceiling). I will finish the interior and exterior siding/roofing.

I realize with this little info it's pretty tough for you to say but can you give me a rough range of the $/sq ft I can expect? I'm hoping to start end May/early June. I can snap/post some pictures if it'll help. Thanx!