Hi - I've built two houses from the ground up. In both cases, I did the complete plans myself, and then had help in building. In the 2nd house, I had a lot of help building. The first time around, I was part of the framing crew, and did everything after the frame was tight to the weather myself. It took 8 years to finish (finish being a relative term!), and I was a LOT younger than today
The 2nd time around, I didn't actually do all that much myself, aside from being my own general contractor.
Having done this, I don't believe there is any good way of figuring costs based on square footage. Square footage isn't the main factor influencing the cost. It's the type of construction, materials involved and of course the fittings and fixtures (kitchen, baths, etc.).
I recently found the "list", with costs, for all of the components of the house starting with the site work. Everything is listed. From memory, it is something like this:
bringing in power and phone service (a $20,000 expense in my case)
site work
excevation (of the foundation)
forms and foundation (including concrete and rebar)
framing (which included the roof)
chimney and fireplace
exterior doors and windows (a BIG cost)
siding (another big cost)
wiring
plumbing
insulation (double wall construction)
drywall
floors (oak)
stairs
floor and stair finishing
interior doors (real wood panel doors add up)
finish grade and landscaping (just grass)
driveway paving (a major expense)
heating system
exterior decks and porches
I took it from there and did everything else myself (kitchen, baths, finish work, except for the floors).
Some items such as the foundation are pretty much per-foot. Even the framing can be reasonably calculated. Other things such as the floors, windows and siding vary greatly depending on what you pick.
Don't skimp on the windows or insulation. Do double walls (I did it, and it's not that expensive) if you can, and use low E argon tripple glazed if possible with most of the glass facing south. Include entrance air locks (2 doors and a small hall). Consider solar right up front - even if you don't install it right away. Anything to make that house more energy efficient.
Use a furnace that goes cold between firings. We could talk about heating system design all day, but since that's not the purpose of the thread - I'll leave it for now
Absolutely include a full foundation drain, beneath the floor and around the outside. Tar the outside of the foundation. Fill the area under the basement floor with crushed stone, and all around the outside - at the footings. Use preforated PVC inside and outside of the foundation and have the whole thing drain to DAYLIGHT. Put layers of thick poly over the stone, under the floor. Put lots of thick poly and construction paper over the stone over stone around the outside, and use sand to backfill immediately around the foundation. You will have a bone-dry basement if you do this right. I can personally attest to the effectiveness of such a system, having done it twice. And yes, water sometimes comes from drain outlet (about 50 feet from the house) during very heavy rains, attesting to the fact that there would have been dampness in the basement had the water not been carried away !
Ventilate that drain system with 4 inch PVC running from the drain, up through the attic to the outside. It will naturally provide some air movement, and if there is any radon, it will be naturally ventilated away.
This is probably a good time to build a house, with building slow at the moment.
Good luck with the project
(and your marriage is solid, right?
)
Regards,
Steve