Blue
Ravenous Bugblatter Beast of Traal
It doesn't sound like you build them from the other direction - I too start with player wants. It's just another tool in the toolbox for filling those in.True. Considering what the characters can do is good design, just as considering what they want is. The ability to consider the characters you're running for is one of the primary advantages of running homebrew adventures over published ones.
On the other hand, I care far, far more about what the PCs want than what they can do. Keeping track of their characters is the players' job, and I am happy to be surprised if they pull some ability out that I've forgotten about. In my experience, building a situation around something the character/s can do is a surefire way to ensure they'll either go in a different direction or forget they can do that thing you're expecting them to do.
I'm not saying I ignore the characters' abilities. I'm just saying I don't much bother to track them, and I build situations and adventures from other directions.