I completely agree with previous posters here that there is no "recipe" for what is a cafe bike just as there wasnt for a "chopper" bike. YOU have to have some ideas yourself and the way to do this is research.....look at bikes/builds on this forum - as someone else said start with Bike of the Month thread and PM people, ask questions....
as you likely know...the cafe bike was born out of the 50`s and 60`s British bike scene when guys with Triumphs, BSAs and Nortons would remove stuff to make them faster and more racier, get some custom stuff made up (like rearsets and clipons) and pull the valve cover to install new springs or do some engine mods (yes they ALSO did engine mods!!!) to ride around London or in the countryside, racing from pub to pub at high speed...I met some of these guys in my time (Oxfordshire, London, Brighton)....they would laugh at the idea of a "formula" for a cafe bike.....
....now today you can do sooooo much with your SOHC bike - there are loads of parts that can fit or be made to fit - looks at Xtalons thread, Bwaller, Tintin, Seawebs, Gordons (Ibikes), Daniels (DME) and a host of others for some ideas...dosent need to cost a lot of money (though usually does) and things to consider are stainless steel brake lines, drilled rotors, clipons/drop bars/euro bars, bar-end mirrors, new carbs or just cleaned carbs will suffice!, rearsets, new seat made by yourself, racier tank?, new rear shocks for better suspension, new front suspension - progressive springs?, engine mods - porting? new cam? valve springs? new studs?, add some chrome/polished engine covers, rearsets etc etc etc........and of course good tires!!!
good luck!
Andy