Campaign help

[SylvaTerran]

Ill try i'm planning on letting how the party act for the first session set the mood for the rest of the campaign. But knowing my gaming group they'll end up evil again so i plan on making them the BBEGs and sending them as members of an organization that will help them and the necromancer along as a story point.
Basically I'm planning to run a campaign where the dm plays the party and the characters play the bad guys.however if they do however go good Im planning on having a awesome level 10 end fight that will involve a dracolich (scaled to level) and about 200 zombies attacking the main city in the world.