How do you intend to "force" a flag to be carried through the enemy base? I don't understand the layout you have in mind. With the high mobility in TF2, tracks are the only thing that can easily restrict objectives without turning the whole map into tunnels.
Well, at early start, there is a small area, like squares, that are dropdowns, but is there that is the flag. After a 25 setup timer, the doors to the enemy dropdown open, and also a secondary route under it, that is acessible by an area a short walk after the spawn, but the same length as the dropdowns.
On the doors that connects the dropdown, that I'm going to call D, I'm going to need something that drops the flag, so Soldiers, Demos, Scouts and Engies cannot exploit.
Also, a door on the dropdown is the way to get out, leading to a lane with plenty of cover, but right next to the enemy spawn. There is a wall separating the bases, with player clip on the top.
On the underway near D, that I'm going to call U, it leads to the lane, with two paralel ways, one leading to RED, the other leading to BLU, on three different positions. But the doors are one-way only, so no chance of exploiting.
Then, the routes reconnect, with a central tower, that is where the point is located, just like Gravel Pit. The area has also plenty of cover, and people might feel more confortable to jump to use the shacks around, and there are also some shacks around the intial lane. The shacks are located in some key positions, with ammo and health.
Anyway, I'm going to send the map to the next gameday when I finish it.