Dungeon Keeper Walkthrough: Flowerhat
The "room of the week" is a workshop. Build the rest and wait for the workshop to become available. Workshops are noisy - put them somewhere they have room to grow and away from the library. You ALWAYS need more workshop room as they fill up with traps and doors and such.
You get bridges, doors, traps and such from a workshop. Learn to do the "imp walk". Build a bridge to where it gets dark, drop an imp on that spot to light it up, and keep building the bridge. There's a level up to the east that you can 'bridge' to.
Train up, find the enemy's heart to the North, and kill it. Build TONS of imps - there's lots of land to take over. Train a bunch. Near the end you'll get "some of your minions are unable to reach their lairs". These are just 2 spiders stuck to the way north across some lava - just build them a bridge. There's a transfer gem up there too - use it at the very end to choose a creature to "bring with you" to the next level.
Dungeon Keeper Walkthough Index