Me and my buddies are really wanting to find some older steel frames and weld them up to create a bicycle for 4 riders. Its really just for fun .... I have descent welding skills. But how should I even begin this process. I've never built a frame? Any diagrams out there for this? I've seen bikes for up to 6 people before ... are they stiff/strong enough?? or do they just flex like crazy. Obviously this contraption will be more for laughs .... 1 or 2 club rides a year. But i obviously want it to be strong and safe .... while not breaking my bank account.