If you follow the right steps, it will be fairly easy to build a door frame. This guide is for making an interior door frame.
Required Tools and Materials 
1"x4" and 1"x1/2" wood stock
Finish nails
Tape measure
Saw
Hammer
Nails
Step 1
Check the width and height of your door. The door opening has to be two and a half inches larger than the door. This is crucial for fitting purposes. This project has a 32 x 40” door.
Step 2
Start by making the door frame top cut. Slice the 1 x 4 is ¾ inches wide and the door is 32 inches, make the top 34 inches. Saw the sides, but you should only add half an inch for the height. This is for the bottom and top of the door. To build a door frame, you will have to nail the sides. Nail it flush to the outer top cut.
Step 3
Measure 1 ¾” on the door frame where the hinge will be set. Add marks around it. Put the 1"x 1/2" wood stock in the middle of the board. Apply finish nails on it.
Step 4
Put the door in place. Put in the hardware. Drill the locks in.
How to Build a Garage Door Frame
Required Tools and Materials
Helper
8 foot step ladder
6 foot level
Measuring tape
Hammer
16 penny nails
Circular saw
(3) 2 x 6 x 10 salt treated lumber
Step 1
Saw the treated lumber to the size fit for your garage door.
Step 2
Join the jamb boards to the bottom and top using the 16 penny nails. Use a 6 ft level to plumb the jambs.
Step 3
Gauge the distance between jambs on the header. Saw the lumber to the right size.
Step 4
Set the header board between the jambs. Set it into position with the nails. You will need a helper here.
Step 5
Mark with a pencil the distance in the middle of the top jamb boards and the header board top. Saw a piece scrap salt to a length of 14 inches. Nail this in the center.
Tips and Warnings
Use only treated lumber. It is more durable than non-treated lumber. Make sure to get more lumbers than what your project requires so you have room for errors.
These two methods show how simple it is to build a door frame. Whichever method you choose, always wear eye goggles. This will keep you safe from potential splinters. You can also don gloves.
