It's not quite as simple as it may seem, unfortunately. It isn't difficult and you only need some basic tools but you do need some clubmaking expertise and experience. For example, you need to know the trim spec for the shaft you're using, you need to know the total weight of the putter you want, the length you want it.

If you're doing it for fun and want to experiment then cool but if you want to assemble it to play with, I'd buy the components from golfmith.com (for example) and get them or your local pro to assemble the club for you. I'm sure your pro won't mind if you watched him assemble it.

I don't know of any on-line "shops" like Golf Smith in the UK. I know a number of club makers though ...

__________________
Golf is easy ... once you know how.
Graham Arnott, teaching professional
Kelrosa Golf Studios
www.kelrosagolf.com
Class 'A' PGA Member
Full Member: World Golf Teachers Federation (GB&I)