Draw chalk lines on the ceiling to mark where the joists lie. The beams must be attached to the joists, otherwise the ceiling may not hold the added weight. Measure the area on the ceiling where the beams will be placed so you know how much timber you need to purchase.
Cut the pine boards to the correct length using a table saw, then cut 45-degree miters on the edges of the boards. Each beam requires three pine boards -- two sides and a top. Clamp the two side pieces with a wooden spacer in between, then attach the top piece using wood glue and nails to create the three-sided box. Repeat this process until you have the required amount of beams.
Fill nail holes and seams with wood putty. Sand the beam with a medium-grade sandpaper and then either stain or paint the wood, depending on the existing decor and the desired finished effect.
Nail a two-by-four timber to the ceiling on the chalk lines marking the joists, creating a ceiling nailer to attach the faux beams to.
Place the first ceiling beam around the two-by-four and attach to the two-by-four with nails. Fill the nail holes with wood putty, then sand and touch up with paint or wood stain.