The Hack platform is so logical that it minimizes the amount of knowledge to be retained to be able to construct it from scratch again using just blank text files
So you could start building all the chips from the nand gate up. If you test each chip with the test scripts, then, if your design is compatible with the Hack computer you should reasonably expect the tests to succeed. This is the case I believe for all the chips with the exception of the PC chip.
This is because the test script for the PC chip includes inputs that can not possibly arise in the working computer.
I think the test should be changed so that this does not happen although it might be better
if the PC chip had one less input.