I am not an expert, and I am just trying to share my experience.
If you are going to level the floor, you may want to level the floor first before putting up the frame. Otherwise, I can see these possible shortcomings:
- If you only plan to finish part of the basement and only frame that area, you will find that framing that area first will make your task of leveling that area difficult because your back or elbows will be against the framed wall when you are trying to level the area near the framed wall.
- You may have problem nailing the baseboard trim or quarter round into the bottom framing wood in area where you have raised the floor with leveling compound or concrete. The nail can easily miss the mark. You may need to add wood block on top of the bottom framing wood as a nailer to get around with this problem.
- Leveling compound or concrete may enclose the side of some of the bottom frame. This makes the bottom framing wood to retain moisture longer than it would be otherwise (in case we have a slight moisture coming up from the basement floor), and may not allow the bottom framing wood to dry. That may or may not be a problem.
If you don't intend to level the floor, you may want to frame it in place instead of preparing the frame on the floor and raise it up. The reason is that the floor may be going up and down having many small peaks and valleys and is not in a gentle slope, and this is hard to tell if the floor has peaks and valleys without using a spring or a long piece of straight wood (I cannot tell just by my eyes). If we prepare the frame on the floor, we may find that the frame may get stuck at the bottom middle section because the floor has a small peak in that area. On the other hand, if the floor is smooth and has a gentle slope, you may be able to prepare the unsquare frame on the floor and raise it up (following one of the tip that Tom in "This Old House" suggested to prepare an unsquare frame). This is probably easier and faster this way (I haven't tried this myself).
Hope this helps.
Jay Chan