I assembled mine using the instructions on ar15.com found in the "Build it Yourself" section. It's pretty straight forward. If you have the stripped lower, the parts kit, and a few basic tools it can be done in less than an hour.
There are some complete lowers out there to be had too if you don't want to assemble it yourself. The DPMS I have was purchased completely assembled and only cost slightly more than doing it myself. The upper was from Del-Ton. After pushing in two pins, a cleaning and some lube, it was ready to shoot. It's been very reliable.
There are some good vendors here that could probably fix you right up.
There are some complete lowers out there to be had too if you don't want to assemble it yourself. The DPMS I have was purchased completely assembled and only cost slightly more than doing it myself. The upper was from Del-Ton. After pushing in two pins, a cleaning and some lube, it was ready to shoot. It's been very reliable.
There are some good vendors here that could probably fix you right up.