Is it Just me or does the OB CS seem less Customizable than the Morrowind CS? I mean in morrowind you could make an interior any size or any shape as the rooms where formed out of parts (Corners,Middles,Halls,etc.) In the Oblivion one it seems all the interiors are just premade and you can't really do much to make them anyway you want. (I am new to the Ob Construction set so can you make rooms the same way in the OB one to?)

Houses became less customizable, yep...You need to get in a 3d-program to tear it up. I think they did it to boosts the fps for a bit, preventive and in place.
There are only a few house interiors that are customizable, and the basemants are usually still free to edit.

Know of any Referance packs that add the peices, I really don't feel like going through and cutting apart each little section.

Depends on what you are looking for. I would do a look over at tesnexus there are several Modder resources over there mostly ruins types some castle I think even some houses but not sure on the last.