Understood but Bicycle makers make it pretty easy for you by listing the equipment and measurements of said equipment under "specifications" or specs. It is there you can find the stem size/type, seat post, Tires, wheel set, component groupo etc. etc. Most of the stuff is not hard to do your own wrenching on especially with a how to manuel. (available on bookstore shelves-even Barns and Nobel) as well as instructions that can almost always be downloaded in pdf form from the manufacture's website. I confess I didn't fool with the crank and bearings on my bike and took that to the LBS to have done by them so yes everyone has their own mechanical limitations. Understood and also Time constraints I could certainly say not everyone has the time nor desire to want to build bikes but if you do you will get much more bang for your buck and will be much happier for it down the road.