Build Custom Bike Yourself

Tach alle along I’ve been riding moped (Yamaha Genesis) for a few years now, so nothing wild, since I’ve been dealing with motorcycles since my youth, I’ve been getting away from this yoghurt cup thing and have been interested in Harley’s and Custom Bikes for a few years. Now my question because I don’t want to buy a “from the pole” I have to build one myself (from the bottom up) I’ve been looking around in the I-Net for a long time to find some pages where I can find good parts get, but find nothing, one of you knows good sides where I get frame, fork, rims, etc. and a side where possibly a “kind of instruction” is or what I mean is a side. where to look out for, for compatibility of parts and regarding TÜV who you understand what I mean Thank you already in advance Greetz BURNER