This is strange but How about the theme Upside down. The Rules and Images Speak for it self. Rules Players must start building from the hight of 255 down all Terrain must be upside down all organics must be upside down all Trees should show the effect of normal gravity all smoke must rise up and cover the upside down terrain or building all plants must show the effects of normal gravity water does not count to the gravity as It will count to the terrain Buildings Must be built upside down if there is a hanging light on the building it must fall towards normal gravity if there are flag they either fly or fall towards normal gravity Basically, Imagin taking an awesome build and turning it upside down the main/normal plot floor should represent the sky Here is an example of what a build should look like. You can find this Island at ./p h _Zetro 2 Overall I think this would be a fun Awesome theme and it will be a very good challenge for players.
This does look like a fun little competition - I will mention it to some of the other staff members and see what they think about implementing it along side the Monthly Build comp.
Concerning Jack's statement, I've already started another build comp event series alongside the monthly one, it's a 30-minute build comp that takes place every 2 weeks or so. As this is an interesting idea I will consider this as a theme for one of those.