Imagine getting a percentage of the sales of a Lego set. The catch? You have to design it first.
Granted, you only get 1% of the sales of whatever Lego set you submit that Lego puts into production as a set, but that could be a nice little payday depending on how popular it gets.
The site you'll be submitting a description and some pics of your Lego design is similar to Kickstarter: you upload everything and have to get 10,000 people to support it by clicking the button beside it. (It's called Lego Cuusoo, and you can get started here.)
Once you've gotten to that level, the suits at Lego scrutinize your design and make the final decision on whether or not it might have a future as an official Lego set.
A couple of tips you want to keep in mind when coming up with your design:
-Copyright. Don't design something that a competing toy brand has the rights to, for instance. Same goes for anything Lego might have to license (unless you've already seen a Lego set featuring that brand or those characters).
-Keep it simple. Including things that aren't available to buy through Lego already means your design gets nixed.
-Keep it family friendly. While the non-Lego Breaking Bad set looked really cool, there's a reason it looked like Legos, but wasn't actually made by Lego...they target the family-friendly crowd.
-A good background story about how you came up with the idea always helps.
-If at first you don't succeed, try, try again. Even if you submit 100 designs and only one gets chosen, you're still making that 1% of sales from it!