Determining rough openings for door framing can sometimes be a confusing task. With the multitude of pre hung door manufacturers, its no wonder there are sometimes mistakes made.
The general rule of thumb being, the rough opening for a normal interior or exterior door, is two inches wider than the stated door size. This has been the industry standard for many years.
In the past few years some exterior door manufacturers have started stapling plastic shims to the door jambs. If your supplier carries this type of doors you will need to make the rough opening 2 1/2"s wider than the call out of the door.
One important thing to consider about interior doors is what type of flooring will be installed? The actual height of most doors is around 6' 10"s. On carpeting interior doors are normally held up off the sub-floor 1/2", resulting in a height of 6' 10 1/2". Solid wood flooring or tile are another concern.
If you use a 2 x 12 header, held to the top plate in an eight foot wall, the height will be 6' 10 7/8"s. This will allow you plenty of room no matter what type of flooring is being laid.
If the door has a sidelight, or even two, this must be added to the width of the rough opening.
Leave trimmers out of interior doors until walls are standing. The bottom plate can then be cut out with a circular saw, instead of making some poor sap run around with a reciprocating saw later.
If you aren't certain what size to make a door opening, make it bigger. Far better for the framing to be 1" too big than 1/4" too small.
Check out the window schedule, normally the rough openings for exterior doors are located there.
Patio doors, whether french or sliding glass, are different from one manufacturer to the next so be certain to check with your supplier.