I like this thread... I've been trying to figure out how I would answer.
The thing is, I never really INTEND to build a level. A cool mechanic or concept just occurs to me so I build those pieces.... usually over a LOT of time. If the mechanic turns out to be fun I try to build a level around it... but by that time, the hard parts been done.
That's probably why my levels have a lot of interesting gameplay - I build them out of a whole bunch of little ideas that were fun in create mode.

