Just buy it - massive fun to ride - I've got two 'funny bikes' & two TT frames that qualify as lo-pro's and although they don't really get me to the next county on a sunday run, they are great for a blast round the city or a quick 10 miler or as a commuter as I'm doing at the moment.
Measuring can be difficult, I do mine by eye - seat post lug height should be approx the same as your normal road bike, TT is variable as the bullhorns & stem can extend the frame to fit, with the seatpost compensating at the other end. I don't think you can really apply the standard measurements of a standard road frame as a base. Just get one that's in the right ball park, you can make them fit - just be prepared for some neckache when you first start riding one :roll: