I came across a very insightful video on youtube by FloridaAdventurers. Now he said he was able to make his for $3, but I went with a thicker material (3.5 mil as opposed to his 2 mil) and I included the cost of the paracord and duct tape, as well as my tarp is a little bigger.
Step 1: How Long Do You Want It?
I measured out my 12 ft, marked it and cut it.
Step 2: Cutting the Angles
I didn't want the angle to be too steep, so I measured in 3 ft from the edge on either side and made a mark. With a very large straight-edge I drew my line from the mark I just made to approximately 1 in. from the top corner. I left the 1 in. space for the duct tape that would eventually hold the center line in place.
Once I had my lines drawn, I used tarp clamps to hold the edges of the tarp together while I made my cuts. Once I cut one side I cut the other and removed the scrap.
Step 3: Laying the Lines
I used some white, Scotch Tough, duct tape to adhere the line to the tarp. The tape itself comes in a roll of 135 ft and cost around $8, which is enough for about 3 tarps. I put tape from about 1/2 in. from the clamp and 1/2 in. from the edge of the plastic.
Once that half of the line was done. I removed the clamp and repeated this process for the other line going to the other corner.
Step 4: The Flipside
One at a time I placed the same amount of tape from center to edge.
Step 5: Ridge Line and Finishing Touches
I placed last rope that would be the ridge line and secured it in place on each point and the center with a small piece of tape. Then, going from the center out to the point, put a long piece of tape. I repeated that for the opposite side of that rope.
With all the lines in place, I wanted to add some extra strength to the edges of the tarp. I pulled out some duct tape that would be long enough for one side and laid it upside down (sticky side up). I gently raised the plastic up and pulled it half way over the tape. I folded over the remaining tape.
After I edged all 6 sides I basked in the glory that was my new 6-sided tarp. Enjoy