*inb4alreadysuggested* (too lazy to read all 40+ pages)
Over at the old UT mapper scene we had several contests in the past:
One was a visuals contest where the mapper should style a preset floorplan. You should create a new style if possible. Sadly this doesn't seem to be very easy with tf2 maps.
An other was a layout contest, where mappers should create a small deathmatch map, with the floorplan resembling a character or a number in any axis, for example a B shaped floorplan or a T shaped Map on the y-axis or whatever.
For TF2 you could either use a symmetrical floorplan for common gametypes like ctf, koth or cp or non-symetrical letters for attack/defense cp or payload (also possible: different letters for 3 stages), this would be up to the mapper.
An other idea i had was one where you can include newbies and pros at the same time:
A contest split up in 2 phases: 1st phase is to create a simplyfied, dev-textures-only layout for a map (any gametype or a specific) without styles/details. Winner is the best/simplest/unique competetive and gameplay-offering layout.
In the 2nd phase, the contestants may choose the best or one of the 2/3/4 best layouts and create a stunning style/setting for it, without any major changes on the preset layout.
Winner could be noobs and pros alike, pros could try to create new settings or use existing ones.
Winners would be 2 people, one who created the layout and one who created the visuals. Or one mapper if he manages to create a stunning layout with a great style and rocks both phases.
Or you make a contest for a simple map on a special gametype. not completely new gametypes, but those where you can use more than 1 intel in a ctf map or where the red team spawns with the blue intel in their hands (could be a nuke bomb which you have to carry to the opponent's base) and the blues vice-versa.
The basic gametype remains the same, only some elements are changed to create a new gameplay perspective without the need to create a full new gametype like PLR.
ofc with the condition, that the changed gametype is easy to understand.
Just a few ideas i had in mind
