One possible process:
Put the illegals that are going to be deported into a military barracks style camp. Call them “alien workers - AW”
Have the AWs make pressed earth blocks: - https://en.wikipedia.org/wiki/Compressed_earth_block
Use the blocks to construct railroads and Border Guard (like coast guard) barracks, etc.
Use the blocks to construct the main wall as well. Wall should be tall enough to defeat most climb/ladder attempts. Should be wide enough for vehicle traffic at the top, with ramps for vehicles to drive on and off.
X number of blocks and you can go back to Mexico border.
X+Y number of blocks and you can go back to Home country.
X+Z number of blocks and you can go back with a clean immigration record.
why would you trust them to make good or even satisfactory blocks for building anything? They don’t care enough to come thru legally why would they care about quality of their work when being an AW as you put it?