If you want to create the look of an old wood beam, this is a fairly simple, and fast way to do it.
1 - Use Standard Pine 1x6s. They are cheap, and already have imperfections.
2 - Using 3 boards, build a 3-sided "trough" that will be mounted on your ceiling.
3 - Using an electric chain saw, completely rough up every surface.
4 - Using a course grit orbital sander, knock off all the frayed wood.
5 - Stain and install!
More detailed explanation in the video.
Step 1: Buy Cheap Pine Boards
The cheapest boards have the most defects, which adds character.
Step 2: Build a Beam Shape
Glue and nail the boards together in a box shape.
Step 3: Rough Up Beam With Electric Chain Saw
Hold the saw at about 15 degrees and drag it over the wood
Step 4: Sand Off the Wood Chips
This is just a light sanding to remove any wood chips that are hanging on
Step 5: Stain
Use whatever brand and color you like. Paint on and quickly wipe off excess.
Step 6: Dry and Mount
Let the stain dry overnight and your beams are ready to mount.