I've tested custom housing a little bit and found some bugs:
Erasing Foundation
With the method multi.erasehousecomp it's possible to erase parts of the foundation. After that SendHousingTool put the player outside the multi and multi.house_editing is true, but the HousingTool doesn't appears. Also multi.acceptcommit() doesn't work, because there is no editing player.
After serverrestart the foundation is complete again, but multi.house_parts.size() says that parts are missing. I erased all parts of the foundation and after restart, it was complete again.
multi.house_parts.size() says, that there are 0 parts and SendHousingTools gives error{ errortext = "You must be inside the house to customize it." }. After erasing the multiobject, the whole foundation is gone.
Erasing Exterior Stairs
When I put an exterior stairs on the ground, erase it and after that click with erasing tool on the foundation, the stairs appears again. Also after commiting, the stairs are back. This affects just the normal stairs, neither decorating parts nor cubes.
Erasing Floor
I constructed wooden floor and erased one part in the middle at first floor. After that, it was possible to see the ground below the foundation. The dirt, which I expected to see, was one field moved. I only noticed that once, couldn't reproduce it.
Several Gumps Closing
After sending the HousingTool to the player, several gumps are closing. E.g. statusbar, paperdoll, backpack.
Additionally here are some features that would be nice, don't know if they're possbile:
No Difference between interior and exterior stairs
It's not possible to make custom stairs with the HousingTool or to put them on the east side of the house.
Scripting your own HousingTool
I think the HousingTool has it's advantages and disadvantages. On my server, we have a already a building tool and after building the house we need to export it to the muls.
Is it possible to have the same behavier (e.g. player can't leave the house while editing, item highlighting, targetcursor long press for many items, ...) with you own gump?
I thought of something like StartEditingHouse(who, multi), after that i can send the player the gump.
Custom Foundations
It would be nice to have your own foundations. I made an 16x16 grass foundation, the height is 1. HousingTool sets the player to z = 8 and all graphics are created on the same level. So it's unusable for my custom foundation.
First question, what pol build are you using ? 03.09.2013 beta ?
Bugs:
1: Havent tested this, need to see whats going on
2: Fixed in SVN
3: Should be fixed in SVN there were problems with dirt tiles created at wrong places
4: Totally clientside, the server has nothing to do with this and it can not be blocked, the only way around this is to resend all these Windows when the customhousing tool is closed ( housecommit or closetool )
Features:
1: Interior stairs are using the stair sets ( multis ) and exterior stairs are using the single tile pieces. Its impossible to Place exterior stairs anywhere else that house.maxy + 1 because the client simply allow putting them only there. The client is also blocking the housetool from putting these interior stairs and exterior elsewhere than right now. So sorry not possible
2: Its possible to stop the player from doing stuff while doing something with a custom gump, but it requires checks in your scripts in every Place possible where you would be able to do something else. A good start would be to attach the script of the gump to the player and then check all the other things you want to ( frozen may help also ). To have custom tool act like the housing tool is much more a pain in the ass to create because you can not update all players mul files just like that so you would have to save it as separate items.
3: The housing tool checks floor 1 always at house.z + 7 so make sure your custom Foundation is 7 z tiles high and it should be possible.