When the skills were streamlined for 4e D&D one of the skills that disappeared was Craft. That’s not to say that PCs can’t create things anymore, it’s just that this kind of task isn’t something you’re likely to use very often. It’s a task more suited for an NPC, not an adventurer.
However, there might still be times when you do want to create something yourself. You might require a unique device to accomplish a goal, you might need to pose as a smith or carpenter, or you might need to craft your own weapon as the first part of an epic quest.
When PCs find themselves in this situation the DM needs to determine just how significant the outcome is going to be. If it’s just something you’re doing during your down time then no role playing is probably required. In fact no roll is likely required either. However, if the success or failure of your handiwork will affect the outcome of things to come, then perhaps it’s time to turn your labours into a skill challenge.
