My wife and I are about to build one this summer from
Pacific homes. Here is the story on them:
A mobile home is exactly that. The entire house was built elsewhere and is brought in and set down on a slab.
A modular home is a home where entire modules are built (e.g. the living room, complete with wiring, sheetrock, painted walls, etc.) The modules are then assembled onsite.
A prefabricated home has the walls built, trusses, etc. They come in large shipments and nothing is assembled except for the walls. Generally you are responsible for putting up the foundation, electrical, plumbing, hanging sheetrock, etc.
We are buying prefabricated for many reasons. First, we sent them our house plan, which is a 3700 square foot custom home with a 900 square foot garage. Ceilings in the home range from 8 foot to 11 foot. They are building it for us exactly as we want. They have an architect you work with about details, etc. The wood used is kiln dried, not Home Depot BS that shrinks and warps. We pick all details, down to what doorknobs, closet doors, shingles, siding, windows, etc. Everything is essentially included to get you shelled in. Our package is coming to about $180K. Add on top of that someone who actually puts it up (because it does take skill to erect almost 4500 square foot building) who is charging around 30K. Then we need electrical, plumbing, cabinets, etc. All in all, I will probably spend close to 400K but think the house will be worth closer to 500-600K.
Prefab != modular != trailer != mobile. Pre fab means that the walls and trusses are built in a controlled environment and shipped up. Please, someone explain to me the difference of a wall being built onsite and erected, and a wall being built offsite then erected.
Edit: Also, since Pacific-Homes uses their own forrest and kiln dried wood, there is no waste. If I want 14 foot walls in one part of the house, they simply cut the 2x6 into 14 foot pieces. 9 foot walls doesn't mean I buy 12 foot boards and cut 3 foot off, it means they cut 9 foot studs.
All in all, you ARE paying someone else to assemble the home for you. If you are a DIY type of person and can frame a house, it may be cheaper to order lumber and do it yourself. Then again, buying in bulk from Canada does seem nice.