If you don't know much about bikes, then you might not really notice the difference between a stock bike and a custom bike. Another option to think about is paying for a custom fitting of a stock/production bike. What this means is that (depending on how much your LBS would charge, it's usually less if you buy a bike from them), they can set you up on either a fit kit, or put you on the bike while on a trainer, and then run a gammut of measurements to dial in your correct saddle hight and position as well as handlebar hight, angle, and stem length. This would give you a stock/production bike that fits you like a glove, and having a bike fit you like that is all the custom you need.