Numbers used and their sourcing:
6.6294cm width per bill
2.61in from upper edge to lower edge, converted to centimeters, x axis (wall thickness)
15.5956cm length per bill
6.14in from end to end, converted to centimeters, y axis (wall length)
0.010922cm height per bill
0.0043in thickness converted to centimeters, z axis (height)
enchantedlearning.com/math/money/bills/one/ OR just look in your wallet
3201km of total border
1,989 total border length between U.S. and Mexico converted to kilometers. Not all of it actually needs covered but for the sake of simplicity, let's use all of it.
rhelp.cbp.gov/app/answers/detail/a_id/578/~/border-in-miles
Estimates for the market size vary and I can't find a concise source to use, so I'll lowball it with an even one quadrillion dollars. Dividing that by 100 for the total of $100 bills gives us ten trillion Benjis.
1,000,000,000,000,000 / 100 = 10,000,000,000,000 = 10^13 = 1 followed by 13 zeros
To cover the border in a single line with one bill height would take a rounded 20,525,020 Benjamins.
3,201km = 320,100,000cm
320,100,000cm(border length) / 15.5956cm(length per bill) = 20,525,019.87740132 (bill lengths per border length = bills per border wall stack)
A single string of bills lined up can be stacked up 487,210 times if you have a total of ten trillion bills to use.
10,000,000,000,000(total bills) / 20,525,020(bills per wall stack) = 487210.2438877039 (wall stacks per gorillion derivative Benjamins)
A wall of Benjamins stacked 487,210 high comes out to 53.213 meters high
487210(total bills in height) x 0.010922cm (each bill's height) = 5321.30762cm = 53.2130762m (wall height)
A wall that's not even 3 inches thick is Jeb-tier though, let's try closer to a meter/yard. The closest amount of wall stacks to a meter thickness is 15 rows of wall stacks, which would be a little over 0.99m. Close enough.
1m = 100cm
100cm(trump-tier thickness) / 6.6294cm(thickness per row of bills) = 15.08432135638218(rows of bills for trump-tier thickness)
15(rows of bills) x 6.6294cm(thickness per row of bills) = 99.441cm = 0.99441m(wall thickness)
The Trump-tier wall would have 15 rows of 20,525,020 Benjamins. The total amount of wall stacks you can build with 15 rows of derivative shekels would be 32,480.
15(rows) x 20,525,020(per row) = 307,875,300(bills per wall stack)
10,000,000,000,000(imaginary Benjamins) / 307,875,300(bills per wall stack) = 32,480.68292584693(bills stacked vertically across the wall)
A Trump wall made of derivative ghost Benjamins would be a little over 3.54m/11.6ft tall.
32,480(bills in height) x 0.010922cm(height per bill) = 354.74656cm = 3.5474656m(total height)
tl;dr
A conservative estimate of $100 bills from the derivatives market could build a complete wall on the Mexican border 11.6 feet high 3.26 feet thick. In all likelihood, it could be even bigger.