fishroe,

Like Buckdropper said 7/16 osb is good for the roof. Yes use plastic for drains and copper for water lines. If possible, and you are doing it, make a main trunk line in a loop and all lines feed off of that. That will stop the trouble of a faucet being turned on and felt at another location. You can shower in my house and turn on all water sources and never notice it in the shower. Make the main loop out of 3/4 with all feed lines at 1/2.
If you want attached garage, detatched should be cheaper to insure, built an entrance room so you have to enter the main house through 2 doors, air lock in a sence, and put a bath exhaust fan in that room to help with the fume prob.
Check around on vinyl siding, look at the mill or thickness as much as price. I dont have it handy, but I will look for the name of the stuff I used. It was very high quality, heavier mill and still at a good price. Ok to use vinyl soffit, but use aluminum facia.
One other thing is windows, it is more than worth the cost to buy the best you can. I prefer Pella pro series, hi R, low E, easy to maintain.

Sled...

 

we had purchased a pella window and installed it prior to the addition. they did not build the window out to speck (about 4 inches too short).

dealing with them afterwards was hell. when we talked to different builders prior to the construction they all recommended anderson.

i think the windows are very similiar in quality, but
anderson has much stronger field support.

mechanically our pella window is fine, but if your doing a big job and need support from the company (sending out a field rep for a problem) or whatever, i think anderson may have them beat there.

isnt all this crap great that you have to worry about when you do this kind of stuff?