Hello I'm an electrician in North Idaho.
I'm not certain if anyone's covered these items yet but I just completed my first new construction spec and here are the big mistakes I've made that that cost me time and money.
1: spend whatever time it takes to double check all the prints from the truss company window dimensions from supply yard and anything else where you have to order the material ahead of time. Also make sure you and the suppliers are using the "same technical language"
2: show up as much as possible when you're subcontractors are working get your tape measure out and check plumbing stub ups door openings Concrete form dimensions and square and really anything else that will cost to be adjusted or impact your project down the road.
3: lastly
if a subcontractor does not meet the preset expectations for completion do not wait around hoping they'll get their act together, fire them pay them out move on.
I hope this helps, good luck it's a lot of fun!