Having not read any responses but.If homeowners houseis that bad. 

Who cares if he's over estimating materials, is his price for the work being done reasonable?

It is designated one of the city "tipping point" neighborhoods.

Thanks for the response and I appreciate the confidence, Jeff!

Some things that might be a concern:1) Obviously have to make sure things are all permitted first2) I don't want the room to "feel" like an addition, so flooring has to be same level/standardized with the rest of the house3) Unlike the rest of the house that has an identically-shaped 2200sqft basement underneath, this added space will not have a basement directly underneath it -- I'm not sure if this poses major cons for some reason that I'm not aware of4) Especially given the lack of basement underneath, I have to make sure that the HVAC can still somehow be piped into this room#2 and #3 are probably my biggest concerns (#1 and #4 I can find out relatively easily)Any tips/thoughts or other experience would be greatly appreciated. 

It will give a response not based on our opinion, but math and analytics based on data. 

My GC is my partner on the deal, he gets 25% of the upside plus his GC fee and I'm 75% of upside. 

Any tips, tricks or suggestions to point me in the right direction?

I truly appreciate you taking the time to read my question and provide a thoughtful response.

His communication with me is terrible.