Okay, the gametype is Forgewar, it is in two rounds at the minimum. the first round lasts 8:00 or until both teams verify that they are finished... Whichever comes first. In the first round, everyone is invincible and cannot cross to the other side of the map, and is in monitor mode the entire time and can build whatever they want. Then once a team is done they can select an option that will start the next round iff all players on each team have it enabled. Then in the second round is like regular Team Slayer or BTB or whatever Forgewar variant you're playing except the stats are all normal and monitor mode is disabled Whadda think?
I think it's a terrible idea. If Bungie thought that it was a good idea, then they would've implemented it in Halo 3. Or ODST. I think it's bad because there could be a lot of flaws. Team members could totally suck unless you're with friends or a clan. One team might be working together to make a good base, but the other team could still be arguing and fighting over pieces. Also, one team could just be really stupid and build an incredibly tall tower, so tall that it overlooks the whole map, and have only one way to get up or down. Obviously this kind of gametype could be unbalanced, unless many restrictions are laid down.
This sort of thing is already played as a custom gametype with monitor enabled for one person who plays god building the map as the game goes on, or with two sides forging a map then the host saves and they play it in customs. Nothing new here besides removing honor rules.
8 minutes per round... and the only way you can do anything is dependent on a single player...? Veto.
I've done this in forge.. You get some buddies and give yourselves time to build a base... two teams of course. You then go into customs, 5 lives, etc... fun as hell.