Easiest to make from scratch is a bolt action stacked tube poppet. The seer is much more forgiving than attempting to do a semi auto.
As far as loading, I think the easiest way to load it is via a straight magazine, so there's no play in the FS rounds (misfeeds/chops sound expensive). If you wanted to make the equivalent of a real rifle that fires FS-loaded solo shells then that is pretty awsome and I wish I had won the lottery to be able to feed it.
What kind of tools do you have access to? What kind of budget? Do you want to make it look spot on like a DSR1? Alot of guys prefer wood because its hand workable and easy to fix oopsies.