What kind of square footage? Odds are good with 3 stories you will not have decent coverage over the entire house no matter the router or access point you used.
With regular stick frame construction, you are looking at MAYBE fair to excellent wireless coverage in a single story house to around 2000sq-ft in size with most access points. Multiple stories can increase the size of the house, SOME, but not a lot. Downside is if you are directly above/below the router by much and you'll get crappy signal because the signal propogates the best horizontal from the antennas and the signal strength drops the further off the horizontal plane you are.
Also other things like metal duct work can severly curtail the wireless signal.
My suggestion is, if you are having the house being build, think of centrally located, but also have several pulls around the house. Such as bedrooms, office, living rooms, basement, etc. Considering the cost of a house, paying $300-800 for a dozen LAN drops through out the house is pretty good insurance. You can always have the router located centrally and then install an access point or two to extend coverage (where you won't need coax).
If its a resonably large house I'd plan on one access point per floor. Otherwise you'll have scenarios where you have the wireless signal trying to penetrate a floor at a very accute angle killing the signal trying to go all the way across the house and through a wall or two to boot.
In my house, with my basement router at the far end of the house I have about 2 bars of signal strength on that router about 35ft from it, through the floor and 2 walls. ZERO duct work in my house in the walls/floors to possibly block anything (attic AC unit) I mean, its a connection, but its a lot weaker than I'd want. I also have a living room AP which I can connect to (and my devices will at that point) that bumps it up to full bars and a very healthy and fast wireless connection on my main level on the opposite side of the house.
Often times unless its a small house or you don't mind a weak connection (IE email and websurfing and maybe just streaming) you really need more than one wireless access point to cover most homes. Especially a larger house or one with heavier duty construction (plaster and lathe, concrete, metal duct work in the walls, multiple floors, etc).