I may have confused myself by reading too many things on the internet
When framing a door (basement finishing), I was planning on doing door width + 2" wide, and door height + 3" high. For example, the prehung doors I found at Lowes are 32"x80". They say rough-opening of 34x82. I was planning on an extra inch to allow for flooring material - so a 34x83 inch rough opening.
If I frame as I said, is this going to be too tight to shim the door? I found other doors at Home Depot that say 33" opening - if I frame at 34" will 1" be too much to make up with shims?
I would rather get this part right than fix it later.
The 82" RO already has about 3/4" for floor clearance.
The slab is 80" (6'8"). the top jamb is 3/4" (or 5/8"). The door slab should be above the bottom of the jamb by 3/4" (or 5/8").
If you are really concerned about the clearance, make your RO 82 3/4" and set the jamb on 3/4" (or 1/2") temporary shims as you install the door.
Remove the shims afterwards.
Having a piece of your finished floor available will help you decide.
Adding 2" in both directions allows for the RO not being plumb/square, etc. There should be enough adjustment with 2" or you need to fire the framer...
Leave 5/8" (or so) under the door for ventilation unless there is a cold air return in the room.
Short of cutting off a body part, the worst that can happen in woodworking is manufacturing really nice looking kindling. --- Quoted from lenaitch