The random dungeon that isn't so random

There is an SNES game I played when I was younger called Breath of Fire II. It was pretty standard RPG fare, except for the bonus dungeon.

Many RPGs have bonus dungeons to explore when you beat the game. Usually, the bonus dungeon has the hardest enemies in the game, and is not related to the story. The bonus dungeon in Breath of Fire II, however, was a Rogue-like dungeon. It was a dungeon that shared qualities with the game "Rogue," namely randomly generated levels with a focus on combat. It turned out to be my favorite part of the game.

Fast forward a few years. I created a Mario Bros. Clone named Super Comrade Oriam that used picture files to create playable levels. I liked this idea, so after I completed Super Comrade Oriam, I decided to create a Rogue-like RPG where random dungeon "tiles" could be easily created by the user with picture files.

That is where the problem lies.

All other random dungeon algorithms I have come accross are completely random. Either the algorithm spawns "rooms" that then get connected randomly with thin hallways, or the tiles to create the dungeon are premade by the designer, so he/she already knows how the tiles could fit together. The best example I found is here, but even this example is too random, and cannot be user defined. I want the user to create their own rooms, as well as hallways, that can lend to an overall style of a particualr set of dungeon levels. So the user can define a large, open dungeon with many columns, not just rooms that randomly sprout off other rooms.

I need to create an algorithm that can read in a tile, and figure out how that tile connects with other tiles. I have decided on some restrictions:

1. Tiles will require at least one "door" that will be an opening for other tiles.
2. Tiles that fit together will share at least one door of the same width.
3. A tile that can fit will be rotated and moved until the matching doors align.

This allows enough randomization to be new and unique every time, but not too unorganized. Because the doors have to be the same width, connected tiles must share some element of the same style. To place a new tile, a random available door will be chosen form the map to consider. When finished, place an entrance and an exit randomly on a blank space. This method poses some problems:

1. How do I determine the width of a door?
2. How do I know if a tile section is unreachable?
3. If placing between two tiles, do all doors have to match?

I must do more research, but this is a good place to start.