I’ve built an extensive series of giant lego minifigs on thingiverse using FDM printers.
Reproducing something like an individual Lego block on any 3d Printer is going to be difficult. It comes down to tolerance and allowance. Lego are some of the best made injection molded parts out there. The tolerances they hold during manufacturing are mindblowing. You may have better luck using a SLS (selective laser sintering) style machine through Shapeways or creating a mold and Resin Casting the parts.
I’ve found the issue is often not your ability to print the block, but you ability to accurately measure the block you’re trying to reproduce. When making these blocks, errors of a fraction of a mm can be the difference between success and failure. Lego’s allowable variation on their molds is 2 micrometers. Thats hard to even reliably measure without special tools.