By the rules, there are no rolls to decide if the crafting works. It would be crushing to spend so much time and gold just for an unlucky roll to cause it to fizzle, and it doesn't really make sense that weeks of work could come down to one roll. Instead, complications can arise or progress can be halted, but as long as the in-progress item can be safely stored, players can resume crafting when they have time. See pages 129 and 133 of Xanathar’s Guide for some examples of complications.
If you really want to be mean as a DM, you could introduce some form of negative to the item when it's crafted, if it would be applicable. For example, using a stolen recipe may result in the crafted item being faulty, as a result of the original owner protecting their recipe from unwarranted use.