[911Rob]

Dan,
I'll help you out with some budget material; but this excercise is not for the guy that doesn't know what he's doing; trust me.

It might cost more for two storeys for a reason?

I'm currently building a two storey house in my development.
The basement is worth about $40,000
Top two floors (main and second) are worth $160,000
With kitchen on main; that'd be about a 60/40 split in superstructure costs.
Our budget is $150/sqft. I've built 11 homes this year, all on budget.
Budget includes site services, home with basement, front yard landscaping.
Many of my competitors are spending $175/sqft for the same home.

If you really, really have to go for this, I'd do the following:
1. Check the foundation and structure is all OK
2. Check availability of insurance/lending/permits (might do this first)
3. Expose the trusses and brace them all together; then lift the roof off with a crane.
4. Apply 2nd floor, walls to re-use the trusses and roofing
5. Yadda, Yadda.

I personally would never do this in fear of the costs getting away on me; but like I said, I'm an engineer and I work within strict budgets and procedures; no unkowns.

Hope this helps?