Tony Taylor:
Start here : http://sheldonbrown.com/
Read every word of this webpage. Commit to your own rear hub axle offset and locknut to locknut width requirements before you start. Even though the internal database is wonderful, I'd suggest investing in a worthy set of calipers to trust your own hub measuring dimensions. Learn to measure your own ERD. Be sure of the cross pattern you want (x3 front x4 rear would be traditional for a 32/40 pair) Download Spocalc. Washers under the nipples shouldn't require any change to your calculations. Happy Wheelbuilding ... it's the skillset that continues to bind us together on this list.
Kindest Regards,
Tory Werne
Woodstock, Georgia USA