Ascertain the planes where the joists lie, above the ceiling, and mark them with chalk lines. If you don't attach the beams to the joists, the ceiling may not hold the beams' weight. Measure the length of the ceiling where the chalk lines are placed, to determine the amount of timber required for the project.
Refer to your measurements and cut three 1-by-4 pine boards to the correct length, using a table saw. Each of your faux beams requires three lengths of wood, as you will be creating a three-sided box. Cut 45 degree miters at the end of each board.
Clamp the two side pieces of the first beam with a wooden 2-by-4 spacer in between. Run a line of wood glue along the top edges of both pieces, the lay the third piece on top. Secure the top piece with nails into the other two pieces where you glued. After the glue dries and before you move to Step 4, remove the 2-b-y-4 spacers, since you'll use them on each faux beam you make.
Fill nail holes and the two outside seams between the boards with wood putty to create the effect of a solid piece of timber. Use a medium-grade sandpaper to sand the beam. Apply a wood stain or paint to the beam, depending on the desired finish.
Repeat steps three and four until you have the required number of beams for your ceiling. Allow the paint or stain to dry completely before you progress to attaching the beams to the ceiling.
Create ceiling nailers to attach the beams to. Nail two-by-four timber to the ceiling on the chalk lines marking the joists. You may use the scraps from earlier, if they're long enough to create a substantial hold on the joist above the ceiling drywall.
Place the first beam over the 2-by-4 and nail it into place, securing it every foot or less. Repeat until all the beams are in place. Fill the nail holes with wood putty, sand the patches when they're dry, and touch the spots up with paint or stain.