Awaz,
A 'Cafe racer' is a pretty open catagory..... And when you say 'build' - what you really mean is "Stuff $20 bill into a small brass cannon and fire until finished".....
That said - if you're looking for something from the 70's that's NOT European (the 850cc moto Guzzi's make good cafe racers), take a look at hte following:
Yamaha:
XS 650 - the early standards are excellent platforms, pre...'76? After that they went with a 'custom' which meant smaller rear wheel, tiny gas tank. The earlier ones with larger hoops look better.
RD Series - yes they're 2 stroke, but they look the part and parts are still around. The RD400 would be my choice, but hte 350's are goo too. There's way cool body work available form AirTech.
SV 600. Great 4S single. A natural.
Kawasaki:
KZ400 - looks almost exactly like the Yamaha above. Same gig - pre 76/77 for the same reasons. Parts aren't as readily available for the 400's as the yamies tho.
KZ 650 Four - these were bargain bikes sold alongside the famous Z900's/Z1000'a and look almost identical to them.
H2 750 - Yes, a 3 cyl 2 stroke. Three motocross engines tied together. I called mine Cerberus (the 3 headed hound of hades). These are now made almost exclusively of unobtainium, but I recommend it over the more collectable 500 as many of the initial chassis issues of the 500 were solved with the 750 - and good thing too.
Honda:
Those already mentioned and two others:
CB 750/550 SOHC - the SOHC 750 had a great racing history and still runs in vintage events. There are many parts avail and lots of good looking body work for a transformation - BUT, it's become very collectable (and to think I used to buy 'em in the shop for $3-400 back in the mid 80's). A good substitue for a personal toy is the smaller 550 cousin. It already looks classi - a set of clubmans, rear sets and a faring and walla - you're in business.
Of course, you WILL SAVE YOURSELF a huge wad of $$ and buttpain if you just ride your skateboard down to the Triumph dealer and buy a clubman outright.