were the upgrades being done on time and materials?

Yes everything has been reasonably on time. We are pleased. But we upgraded from single-pane windows to double-pane with prairie grids. At one point orally he mentioned there being a $900 difference between what we chose and the spec house price. On paper, he's asking for $1200 and refuses to show us the window invoice. It's happening more and more with items (paint, etc). I just want to know if I have a right to the invoices or if he just has me over a barrel because he has my earnest money (non-refundable) and a contract?

A time and materials job requires all receipts to be turned into you have you paid home for the rest of the job