I use a huge Chessex wet-erase battle mat to draw maps from published adventures on and I'm currently running The Lost Mines of Karak Lode. It's, by far, the largest map I've had my party play. It's so large that I can't fit the entire map of one floor onto a single battle mat-- and there are two floors!
Since my party has the option of taking any number of paths through the dungeon, I can't anticipate which rooms they'll go to first. Therefore, I can't only draw selective parts of the dungeon.
My only idea at this point is to have everyone sit down to play, draw the room they're currently in, and ask them which direction they'd like to go in. Once they decide what door, hallway, etc. to go through, I'll then draw that part of the map. The only thing I don't like about this is that it really holds up play. Especially if I have to draw a large, complex room, this could pause play for as long as 10 minutes.
Does anyone have any suggestions or ideas to help me overcome this issue?