Warmoth sells the parts only, they don't offer any asembly service at this time. You can have the finish the neck or body if you like, but you will have to put the guitar together yourself of find a good tech to do it for you. Their parts are first quality and the results can be excellent if you know what you want and have the right person putting it together.
It's very habit-forming. I'm on #20 now. Shovelhead is right - my first was a LP and with the longer-scale neck. It was a nice axe but did not feel or sound like a Les Paul. I've done a LPS with the shorter-scale neck and it's a lot closer to the right feel.
Warmoth is great for parts, but like Shovlehead says it can get expensive really quick when building your own entirely from Warmoth parts. I've priced it out many times and I can always get a good, new brand-name version for about the same money.
Where Warmoth becomes a great value, to me, is when I need a replacement neck or body (for example) to fix or finish a kit I already have part of.
joolzriff, have you played a Custom Shop Strat, yet? Once I did I've never looked back. Not sure you could even get close to a great Fender CS Strat with Warmoth.
To build a top quality parts guitar expect to spend +/-$1,000 (yes you can go a little cheaper if you don't need nitro paint, top brand of bridge, ultra light weight body, top custom hand wound pickups etc). Don't do it if you can find a standard model that works for you. But if you can't, they are a great way to go. I am on #4 right now and I am loving it.
Add $120 for a Callaham bridge, $50 for tuners, $25 for a pickguard, $200 for a set of pickups, and another $50 for additional hardware and paint. You'll have top-notch parts and less than $800 invested. But you have to want to do the work. If you do, and you can do a nice set-up job, you can wind up with a strat that plays and sounds considerably better than, say, an American Standard. (IMHO)
I wouldn't say that Warmoth necks and bodies were too much inferior to Fender CS. I've had plenty of both and feel that the Warmoth quality is extremely high. The advantage of Fender CS is that you can play a finished guitar and know what you're getting. They are also often nitro finished, usually very well, too. The Warmoth finishes are on a par with any American series I've seen.