Very simple concept, would go on a map like pinpoint or classic gen
You have 15-20 minutes to build a fortification. There is a large unbreakable wall in the middle of the map. Can't dig under it, can't shoot through it. Forces you to either build or waste your time standing around. After those 20 minutes are up, wall comes down. You can either fight or continue working on the fortifications, however now you can come under enemy fire. Then the match continues like normal CTF.
TL;DR: SCREW YOU, big wall, build for 15 minutes, fight.
Any thoughts?