I am sure many of you are familiar with the iron chef format (plus maybe the spoof of it done in Order of the Stick), if not essentially you have a number of ingredients and the participants have to make whatever dishes they can from those components.

I suggest something similar for an encounter map, choose say half a dozen items that the map MUST include (either just name them or also provide clip art that may be used should the entrant wish) then all other parts of the map can be chosen as they wish.

Bonus points for some sort of background story linking all these elements into a setting for the encounter.

Suggested list would be something like:
An Altar
A barrel
A Goblin
A trap
A bridge