Oops, I just caught the small print. A "Factory Built" home has many advantages over a "Site built" home. It's built in a climate controlled environment using kiln dried lumber that won't warp and will not be sitting in weather for months on end.
The standard in today's FBH is a 2x6 exterior wall. All the insulation under the home, in the exterior and bathroom walls and in the roof meet and/or exceed site built homes. They have to be manufactured to the same standards as a site built home.
You can spec in any and and all of the same features i.e, granite counter tops, tile floors, upgraded appliances, drywall interiors, stucco, cement, wood or any other type of exterior there is available. You can pitch a roof to meet snow loads and you can use any of the same roofing materials you can use on a site built home. Bottom line they are built just as good or better as any stick built home on the market.
The biggest advantage of all, however, is turnaround time and ease of set up and installation. A Factory Built home can be completed in weeks vs months and you don't have to tie up you jobsite for several agonizing months, have material and supplies sitting around getting weather damaged or getting legs.
The factory is your free architect and engineer all rolled into one and some factories i.e. Silvercrest Homes, which I happen to be a long time dealer and installation contractor for, http://www.silvercresthomes.com.
will even let you design your own floor plan and select any upgrade your heart desires.
Lastly, you don't need t worry about all the inspections you would if you were to build a site built home. The only permits and inspections you will need with a HUD approved "Manufactured Home' are your plot plan, grading, utilities and infrastructure permits. All the construction permits are done when the home leaves the factory. Hope this helps.