Depends if your going to wrap in wood or drywall. A wood wrap is going to require a 50" x 82" rough opening. 1/2" drywall will require 49 1/4" x 81 1/2" rough opening if your using drywall bead prior to fininsh. However, not all bifolds are built the same, most bifolds are 79" in length, some are 80". You will need to an inch to the above if your bifolds are 80".