i didnt meant that you cant get out, but if the walls have many HP, then the catapults/other siege weapons could have more damage against it.
also, your idea is good. the 0 walls are quite easy to make, and the 8 walls could be something like the castles (so you can go inside of it). the problem with this, that the enemy can cross these "open" points too. there is also the rotating problem, what makes hard to build it in specific places. also, it has not much use against the flying units, but why are the tower of souls? which faction will have this wall?