One thing I found fun was to start by blocking out one room, then another and another and basically switching between tools - the geometric shape too for a tower or two, and then start linking them up.

After a little bit of noodling you start to feel the outline of a building and then you can be a little more deliberative.

In my experience, the hard part about planning out a dungeon is filling it with encounters.

There's another creator (Donjon) which doesn't make maps as prettily or easily as this one but it does allow you to basically do what you're looking for:

https://donjon.bin.sh/d20/dungeon/