The first step in this set of free woodworking plans is to cut the rails and stiles for your particular set of louvers. However, since each installation is different, you'll need to know some principles before you can begin your layout.
Each slat in the louvers will cover one vertical inch of space. We'd suggest that you leave a 1/8" gap between the top and bottom slats and the corresponding rails. For instance, if you have approximately a 24" tall opening for the louvers, you'll want to make the opening 24-1/4" and insert 24 angled slats at one inch intervals. Additionally, each slat will be inserted into a 1/4" deep groove in the stiles, so the slats must be formed as 1/2" longer than the width of the opening.
Once you know the dimensions of the door, window shutter or other installation, you can determine the length and width of the rails and stiles. Use your best judgment as to how wide each of the rails and stiles should be ripped to maintain the integrity of the entire unit.
As an example, in the case of the louvered window covering we built as a prototype, our opening was 30-5/8" tall by 23" wide. As such, we made our two stiles 30-5/8" x 2-1/2", and our rails 20" (to accommodate a 1" long tenon on each end) x 2-11/16" wide. We cut all of these parts out of a very straight, clean 2x4. (For a louvered door, you'll likely need to use stock thicker than the 1-1/2" width of the 2x4.)
These rails and stiles left us with an opening of 18" x 25-1/4". This means that we needed 25 slats of 18-1/2" x 1/4" thickness ripped out of a second 2x4.
TIP: Be sure to cut a few extra slats, as you'll likely want to cull a few that have some knots or other imperfections.