Our house is a metal building; very strong and looks good too.  The best thing we did was put in a laundry room with two washing machines; one for work clothes and one for town clothes.  The washer for work clothes is right beside my shower, so I use it as a hamper between loads.

 Install lots of outlets, and lots of lights.  Your eyes will get older faster than you will.

Get some chalk and draw out your design full size on a floor or the ground before you build.  It's surprising how little things show up in full size that don't occur to you when you look at the drawings.

Plan for three-way switches anywhere you think you may want them.  It's far better to have a few switches that you don't use much than to wish you could turn off the lights to a room without having to walk back through the dark.

Be sure your marriage is in good shape.  If it isn't when you start, it will be in tatters before you are done.  If you don't think you are up to the strain of building a house, hire someone to do everything, and stay away from it until it is time to take possession of the keys.