If you use a conversion cassette, make sure it will work with that particular wheel. Some wheels the dish is wrong and you will hit the spokes when shifting into your largest rear cog. Depends on the wheel, but WheelsManufacturing gives a list on thier site.
If you can afford to build the bike you are talking about, you can afford a Campy-compatible wheel. Just buy the wheels and Campy cassette and forget about it.