Megadungeon design can be a tricky beast. Coming up with hundreds of ideas on paper and the detailed maps to go with them can be a chore for something that is meant to be fun. Beddo over at Dreams in the Lich House made some decent observations on the topic recently. Node based seems to be a way to go.
For my MOG campaign I use a node based approach myself and find it an easy way to make a big dungeon seem really big. The node based design has also freed-up how I draw my dungeons maps. I've used digital maps, two different types of graph paper, copier paper, and notebook paper all at different scales because I don;t have to worry about mapping things the same way for each node,,, I'm even free to get a little funky thanks to the node design.
I don't know how big my Megadungeon has gotten. It's scattered on a large number of sheets. A few of the nodes have a separate map and key while most have the descriptions on the map. For a node I usually only worry about where it is in relation to other nodes, write up a hald-dozen or so important rooms and do the rest with random tables as needed. Rooms gain and lose importance in play.
Funny thing is with the crazy mess my players (in committee not always alone) can navigate from the entrance to the ghoul halls and beyond that to a morlock colony, they suspect they know a route to stingbat caves, and now how to find an area of the dungeon claimed by a couple dungeon-gangs all without a map of their own. sure they can get lost now and again but have been able to find their way back to familiar terrirtoy without much trouble.
Not sure if my players have caught on to the node based design just yet but it's working out so far.