I'm not sure what you mean by "DIY from Harbor Freight tarp"
I have taken teens out camping using the cheapy blue tarps
that run for less than $7.00, ($4.99 on sale now) without any DIY work.
The one linked is 7'4"x9'6" hung by the grommets on the diagonal would yield a 12' ridgeline that would cover any hammock out there. No work to it other than tying on 4 lines, (2 to hang it and 2 to stake it out).