That's kind of curious, not a single reply to what I thought would generate some comments....... Oh Well.
More importantly I got an email which verifies that I have finally entered the realm of non-linearity! For me this is a BIG thing. The most important point that has been brought up to me has been the lack of adventure and exploration in my mansions. You need to go here, then here then collect a key for the door that's in your way, etc., etc. The question has been how to break out of that line of thinking and it was Matt who inadvertently brought me to the solution. For those of you who have played Ghosthunter as soon as I type the next word the light bulb should go off.
Mazes.
Take a look at GH and you'll see the hidden maze structure almost immediately. Why is that good? Because if you think about it, when you go to solve a maze you EXPLORE different paths through the maze. Sure, if you're some kind of puzzle solver you'll be able to take the shortest path through the maze BUT you'll miss some of the other paths. Now take that concept and build a mansion on top of it. You have a critical path that allows you to enter in one spot and exit in another. Along that path you put obstacles, difficult situations, doors, electricity. Now you start to scatter the things you need to get thru off on non-critical paths. You hide secrets, gold, shields, keys, whatever on those paths. You can also add sub goals as well. There's a backpack but there's a green door in the path to it. You can totally ignore it but then you don't have the highest score possible. Hide a couple of secrets off the main path and your player may complete the mansion but without 100% secrets.
To develop GH I started off with a maze built by a FREE internet software package (remember Matt) at:
puzzlemaker.school.discovery.com
Using this tool I specified how many cells wide by how many cells high I wanted the grid. I know, BORING, a rectangular maze. AHHhhhh, but what if you generate 3 or 4 mazes and overlay them so the exit of one coincides with the entrance to another! Now you have an irregular shaped maze that although it still looks like a maze it's starting to become something else. Plot your critical path thru. Now start moving walls around to get rid of the mazish (is that a word??) look. Work your critical path and then start on sub tasks/sub paths. Pretty soon you have something that no longer resembles a maze unless you look carefully.
At this point I start working the graphics in and make the structure of each room work by itself and also with surrounding rooms. From this I start looking at the map views to see where I can move or eliminate walls to make it look less and less like a maze.
PHEWWwwwww, long post....
I am not saying this is the ultimate way to layout a mansion but for me it broke me out of the room at a time thought process that always seems to have put me into the linear mode. In the past it always seemed to be start with a room here then make a room over it and then maybe a room to the left then up again and bang, back into the linear path driven mode. Actually Helter Skullter was the first prototype built on a maze but then I expanded GH to multiple offset mazes. Instead of the path driving the design I found I could now look at the maze and say, It would be very cool to make this into an overhanging terrace because it kind of looks like one or this long passage looks like an underground tunnel.
If you're in a designers block mode, try it! You may wind up throwing it away but I can almost guarantee you'll be past the block and whole new ideas will suddenly pop up.

Happy designing and building all!

Joe B