Intro
Framing a doorway is similar to framing a solid wall, with a few added elements. Like the rest of the wall, it is easier to make a rough opening for a doorway while the wall is flat on the floor, if you have the room. Select the straightest studs you can find for framing doorways; this will avoid problems later.
When you build the wall, the bottom plate runs across the bottom of the doorway. This keeps the entire wall in one plane as you install it. To make it easier to remove the bottom plate under the door, cut most of the way through it in the correct places with a circular saw. Do this before installing the studs, which later won't leave you room to make the cuts with a power saw. After the wall is anchored securely, you can finish the cuts easily with a handsaw and remove the plate from the door opening.
Prestart Checklist
Time
About 1 hour
Tools
Tape measure, layout square, circular saw, handsaw, hammer, level
Skills
Measuring and marking, crosscutting, driving nails
Prep
Determine the size of the rough opening
Materials
2x4s, 16d, 10d, 8d nails