I thought of an idea that i have tried to do in Halo 3 many times but it never worked well. Its 2 seperate maps. The 1st is a Covenant HQ. Covenant HQ -Infection Zombies spawn up top and must make their way down to you and potentially kill you. While you must get to the Hornet up top. Humans spawn at the bottom but one will spawn next to a Hornet. The pilot must assist the players by shooting through the various windows. Then the pilot will pick up humans at the top.Zombies would have shields and they would spawn with an EnergySword and Plasma Pistol(To take down Hornet if needed). Covenant Recovery -VIP This map will carry on from the last, The Squad can drive the Hornet but the VIP cant get on. The VIP and whoever wants to protect him have to go into a seemingly never-ending amount of tunnels in order to get to an evac station. There are some open plains and aesthetics (e.g Graveyard,Bridge etc) for the Hornet to shine! However the enemy team have a higher damge resistance. They cant pick up weapons either but they spawn with an EnergySword and Plasma Repeater. VIP team have 200% damage resistance.
If you intend to build this on Reach then it will not be possible. In the first gametype you said that one human spawns on the roof with the hornet and is supposed to cover his allies. This is a problem because the driver of the new "falcon" can not shoot. There needs to be an extra player to man the guns on the side. Also you said that humans need to get to the top. But what if they decide to camp at the bottom? You need to implement some game mechanics that make the team move. Also, what happens when they do get to the top? Will the game somehow end? Or do humans just get access to an overpowering number of weapons? Please think this through a bit more as it has potential. As for the second gametype...well...there is no VIP mode in Reach