Very do-able. You can end up doing one of three things: buying inexpensive parts and ending up with a dirt-cheap rifle, buying quality parts and ending up with a rifle that is better than most of the mass-produced rifles and costs about the same, or going full-on high end and spending more money, but getting something that is pushing what you can get from the custom makers.
The only part that is not really kitchen-table doable is installing the barrel, but even that is not too hard. Or, you can order a pre-assembled upper and just build the lower.
As to where to go, arfcom probably has a building FAQ.
Mike