Look for twisted studs. Look for shiners (plywood nails that missed their framing target- in floors, they squeak).
A bit late to measure rooms for square. See that any blocking for later installations are there (this could be closet hardware, bath hardware, cabinet mounts, etc, etc). There should be some kind of drywall nailer at wall and ceiling corners, (can be continuous or "ladder" blocks). Really great insulation jobs caulk the plates to the plywood subfloor, and eliminate nasty air infiltration.
If you have the door schedule, verify that the rough openings are correct.
The inspector will catch missing joist hangers.
The low-hanging I beam indicates that if you don't want a dip in the ceiling (we had a thread on this last month) it needs to be furred out.
Feel free to add what I missed, guys.
Casey

Every room must be square. Rather than measure diagonals, you should start from an outside wall and establish a baseline. Then measure each end of your inside walls to establish parallelism.

Next, each wall must be plumb. Your level should be AT LEAST 6' long.

Next, run a string-line across the middle of every wall to see if any studs are bowed either in or out. Don't worry, unless you used steel studs, there WILL be some that need adjusting. If they stick out, you true them up with a portable power planer. You simply plane off the high spots. If they are bowed in, you must add layers of thin material to build them up. Building supply stores sell 1-1/2" wide asphalt strips especially for this purpose. However, ripped strips of 1/8 plywood works better because it will never "relax" like the asphalt paper does.

ONE OF THE MOST IMPORTANT CHECKS IS: Make sure the door openings are PERFECTLY plumb and PERFECTLY in-line. If not, hanging the doors will be a nightmare.

Correct any square and plumb problems now! Once the plumbing and electrical goes in, it will be a lot harder to correct. Depending upon how long it will take you to drywall, you may want to wait until just before the drywall to correct any problems with the studs bowing in or out. This is because the studs my continue to twist and bow.

Everything should be close to perfect. If it isn't, fix it now. If you let it go, you will regret it. Every finish detail will cause you grief if walls are out of square or plumb. Especially things like tile, hardwood flooring and door jambs.

Go around each bathroom and closet and determine where you need backing for TP holders, towel bars, clothes hanger poles, etc. Any wall hanging bathroom basins? You MUST have backing in the correct places. Put it everywhere you think you MIGHT need it. It's cheap and easy and presents a difficult problem if you need to hang something on the wall and it's not there.

As far as the steel beam hanging down, you may need to cut 1/4" nailing strips to bring the drywall nailing surface down to that level. Talk you your drywall guy about it. He will tell you exactly what you need to do.

First make sure it was built according to the design drawings. Check the lumber/panel grades, number of header jacks, nailing, and hanger sizes.

I assume this is a owner-managed project or a custom-build.

For non-bearing studs that are bowed one way or the other, there are different remedies. Often carpenters will make diagonal cuts on the offending side, bang it plumb and renail above and below. Where necessary, I have twisted studs removed and replaced or sistered.

I see this oversight regularly in finished homes--a bathtub at the end of the bathroom that is an inch or less shy of the width of the room. It looks much better to catch this in the framing stage, then shim out the framing so the tub fits flush.

A good drywalling crew will take a look at the house before boarding and advise the contractor of what could be improved.

Here is a link that might be useful: Framing Red Flags