Sadly, Build-a-Coin is no longer maintained. It may still work for you, though!
Build-a-Coin tries to cut down on compile errors by rejecting inputs that would break your new coin. Limitations on input values are as follows:
Build-a-Coin attempts to always produce correct code. If you haven't edited your code at all and have ruled out a build system misconfiguration, please email firstname.lastname@example.org with the following:
If you put unreasonable values in, you'll get an unreasonable coin out. Build-a-Coin coins have been tested for correctness with reasonable inputs, but are not guaranteed to work. If you believe you've found a bug in Build-a-Coin itself, report it to email@example.com.
Build-a-Coin does not provide any support for the compilation process; there are many guides freely available that cover this topic.
One user has suggested this YouTube tutorial series for a walk-through of getting your coin up and running.