I have one that is about to start construction, but I had a few snags during design and bidding - one was the prefab system varied by manufacturers and was an open bid, so was hard to make CD's so that everyone could bid. I just chose one manufacturer and went with thier components thicknesses. The other manufacuters will have to match these components or maybe we will have to change wall sections once we award the bid.
The other messy part was spelling out who does what. Seems like I had to convey a lot more in terms of verbage on the CDs as to who provided what.
All in all, I am pleased with the project up to this point. It is a SIPS panel stucture, should go up in just a few days, and won't have that metal building look, it will look like a framed building. It was very cost effective and saved tens of thousands of dollars. I don't foresee any problems with transport, offsite construction techniques yet. What do you mean by these?

I've done both prefab's SIPS panels on housing and completely prefab modular houses. The SIPS are pretty much just like regular frame construction, just a little more shop drawing review and more coordination. Be aware that they do not coordinate the panels with things like kitchen sink plumbing very well. (this was on a 200 unit developement), so there is some work on the site where the plumbing stubs conflict with the panels. It is definitely cheaper and makes the construction go much faster.
For the completely modular houses, you need to thing modular from day one with the house design. Go to a factory to see how they build them and what the 'rules' are. We did about 10 modular houses. They turned out just ok. Not really any cost savings. The units are a mess when you get them, contrary to the manufacturers promises- lots of nail head pops, whole units had to be repainted. Lots of work to do on site with the trim and siding, roofing, etc. You still have to get up on the roof and patch in the roofing, do second story trim, etc. It is hard to get anything other than average quality out of a modular company. These were 'affordable' housing units. Given the constraints, I think modular still has a way to go. Disadvantages; limited design options, not easy to make accessible, must do a basement or crawl space, average to poor quality when delivered, disagrements with the modular company as to who was responsible for what versus the onsite GC. Advantages; you can build quickly in bad weather.

Thanks for your input. I researhed sips at a design center when I was in school. We were actually trying to engineer an efficient weep hole system...unfortunately, the sip maufacturers that provided us with research info kept going out of business.

Also, when I mentioned offsite construction, I meant constructing the units in a warehouse or factory, instead of ground up construction on the site.

What about recycling old building materials and incorporating them into the design? I see so many interesting prefab designs, but they seem very specific and individually designed. I haven't seen many firms that apply apply a kit of parts method to accomodate ech clients specifications, but still efficiently adapting typical building materials and methods.

Anyway, thanks for the input!

There are 'kit of parts' designs. It's modular, after all, so you can do anything with the 15' width, 50'+ length.

You do need to know that it'll be prefab from day 1. The project we are working on now, we will not have to produce any CDs. This saves the client money and we know that the manufacturer will get it right and be responsible for it all.