Depends on who's frame you get. They are all different in the amount of completion required.
Usually they require cutting of the frame rails, reaming the holes to proper sizes, cutting the barrel lug slot, tapping the grip bushings holes along with the usual work required to fit parts.
Tannery shop is a good start to find the frame. They have a few different versions with varying levels of work required. They also carry KT frames which only require cutting of the rails and the lug slot. If I remember correctly, all holes are reamed to size and the bushing holes are already tapped. They do have an accessory rail on the front, but you can remove that if you don't want it, other than that is is a GI Government model.
[url] www.tanneryshop.com[/url]
[url] www.kristitool.com[/url]
I'm sure there are a few other suppliers manufacturers out there, but these are the only ones that come to mind.