Here is a bifold base that will cut down on wasting duct tape. This base will create clean top edges, and a thin area in the design for easier creasing.

Step 1: Materials

-cutting mat
-flat surface
-hobby knife
-ruler
-duct tape

Step 2: Cutting & Laying Strips (outside Color)

-Cut a 9 inch strip of tape.
-Cut two 9-1/4" strips.
-Cut two 9-1/2" strips.
-Overlap the 9" by the two 9-1/4" (These should be laid sticky side on the mat, and they should overlap 1/8" to 3/16" of the 9" strip)
-Do this again on both 9-1/4" strips with the two 9-1/2" strips
The overlap of strips should be the shortest in the middle overlapped by the 9-1/4" on it's sides and the two exposed edges of those should be overlapped by two 9-1/4" strips.

Step 3: Peel

Peel the duct tape from the mat carefully (make sure when the tape is pulled up that it is pulled up as one sheet, and not as 5 strips). Set this aside.

Step 4: Cutting Inside Color

Cut 4 strips that are 10" each.

Step 5: Laying Strips on Sticky Side

Imaginarily (yes I made the word up) split the sheet lengthwise in half (parallel with the overlap lines not perpendicular).
-Stick a strip of the internal color matching up with the edge of it to the imaginary line. Make it smooth by pressing the air out from underneath.

Stick another strip by lining up the edge 1/16 of an inch away from what was the imaginary line to what is the previous edge stuck down. IT IS VERY IMPORTANT THAT THIS STRIP DOES NOT OVERLAP THE PREVIOUS STRIP. MAKE SURE THAT A LINE OF WHITE/GREY SHOWS BETWEEN THE TWO STRIPS. This gap allows for the bifold to bend without force. It helps with warping problems too.

With the orientation of the sheet being horizontal: Cut a tiny slit or fold 3-1/2" from the middle line on the top right side. Do this for the left as well. Line up the edge of one of the strips with both folds or both cuts and stick it down. Smooth it out. There should be a little bit of tape sticking out above this. Fold this over on the most recent strip that was applied.

Spin top to bottom and apply the same technique to the incomplete sticky side. To make the outside edge cleaner looking, instead of 3-1/2" marks make 3-3/8" marks.

Step 6: Final Cutting

Cut off the extra edges to size the bifold as 9" in length. Be careful not to cut too much off as it will impede how much can be put into the wallet.

Step 7: Another Way of Cutting

On my drafting board I have a ruler taped down to be a little less than 4-1/2" away from the edge. Instead of exactly cutting the fabricated ductape to be 9" I fold it in half then I slideit under the ruler and tape it down, then finally cut it down to the correct size. This way cuts down on the time and effort to recut the edges after it is folded and almost fully assembled.

Thanks for reading! If you have any questions leave it in the comments.