Framebuilders - Building a surrey?

My father wants to build a surrey. You know, like a 4 person bike, kinda like this. (http://www.surreycompany.com/limousine.htm)

He and I both have a moderately proficient knowledge of mechanics (he used to be a car mechanic before deciding to become a lawyer), and have a half-ass understanding of design/weightbearing/etc...

My dad is working on the assumption that we can built this from a couple of goodwill/CL donor bikes and some steel bars and whatnot from Home Depot. Plans on using an airframe/ multiple A-frame type construction to make it strong.

But we've never taken on a project like this. We have no real specialized tools other than what we'd need to cut the steel, and weld. No frame jigs, alignment tools, or anything else.

Is this project doomed before it even starts? What are possible pitfalls? Safety concerns? Is this really doable?

Well, let me say first off, that I've never actually ridden one of those surreys. But from what I read, they are slow and awkward. That being the case, yes, you can almost certainly duplicate a commercial ones.

When looking up some photos on them, it looked like they are normally rigged up like a tandem on each side, with each side driving its own rear wheel. The obvious place to start would be with old tandems. Only, they don't come as cheap as single bikes, and it could take a while to get two donor tandems that sort of matched. Also, these normally use 20" wheels, which are not what's on a tandem.

One other point to keep in mind is that the things are wide, and if you get on a road, you're going to "take the lane" whether you want to or not. And, on a bike trail, you may take ALL the trail. (I've discovered this with my Worksman front-loader tricycle.) So check if you actually have a good place to ride it before building it.

I've thought of this. Dad would want to ride this on the street. It would not fit on the MUP, and will certainly be slow and awkward. He has his proper road bikes for when he wants fast. He is imagining that the surrey would be a funny way to get to work and back every day (despite the fact that he's got a great commuter bike with rack/panniers, etc...). Yes. Impractical. I know. But hey, this is about fun, not practicality.

My dad's the type of guy who gets REALLY wrapped up in an idea without thinking it through, so I hope to give him a few weeks to calm down before he starts a this project. That way he can think it through.
Good point about the 20" wheels. Hadn't thought of that.

Thanks for the advice.