Once goal and requirements are defined, and some ideas have popped into your mind, it's time to have an early confrontation with other designers or the rest of the team that will be in charge of developing the feature.
It's never early enough to share ideas! The earlier you start brainstorming and sharing, the earlier you'll be able to catch pitfalls in your design or evolve your ideas to a more effective level.
Don't think that this part belongs to you. What you are thinking might be not feasible for technical reasons you're not aware of. Get the rest of the team involved!
Game programmers are the most important interlocutors at this point. They are the ones who will implement your design. You want to get them ...
