I like the Modular Home concept and have worked on several. However, if I were doing anything other than a ranch, I would have a builder do it.
Floor Plans - All American Homes

This is company that promotes DIY and this link is a house a friend bought and we put it together.
Modular Homes by SPARTEC, LLC - Two Story Homes - Salem Model

Techniques are different when assembling one of these homes but it is simple and straight forward. The house we put together was finished and occupied 41 days from breaking ground. IMO impressive as it was our first time doing something like this. 90 percent of the assembly was really, "thats all you gotta do?". Most of our problems were with delays caused by local building inspector. Of course a really good crane operator would have been nice to have. But it only took us 3 days to have the house assembled and ready for siding and roofing. Plumbing and electrical were less than a day each and the Heating and A/C guys took 2 days mostly because they could not follow simple instructions, I honestly feel that after foundation is done, with the proper communication and cooperation from building inspectors this house could be occupied in 2 weeks from start of assembly,