Overview:
House with doors everywhere around outer walls and none doors inside looks strange. Not to mention that exit portal is now always "outside", because it should be actually placed in garden. It means anytime you go to your house you need to open door to get inside and it is pretty annoying. Ability to choose where we want to have door, where solid wall, where fence or gate (in case of garden) or where nothing will make things to look much better. Also ability to define doors and gates default and actual state - open, closed or even locked - will help to make door looking more realistic and useful.

Suggestion:
Allow players to build doors/gates/walls/fences (and portals, however) in door space. Both doors and obstacles can have different quality/appearance - plain solid wall, decorated wall, wall with window, solid glass wall (yeah, winter garden!), solid oak gate, metal bar gate (yup, create your own jail!) etc. Context menu for door space can have "build room" and "build doorspace" options to let player choose what he want to do with door space.

In case of doors and gates (and may be also windows) add ability to setup their default and actual state from context menu. The basic set of possible states are "open", "closed" and "locked" and eventually "barred" (can be unlocked from inside only). The default setting can be done by choosing "set actual setting like default" from context menu. Context menu will also contain "open", "close", "lock", "unlock" and "picklock" options. Default option for left click will be choosen according to actual state of door/gate. Only house owner can set defaults and lock and unlock door. Visitors can open, close and picklock only.

But it is possible to have more advanced settings and states. "Open" and "closed" are just basic states. Then there is door or gate mode. In gate mode door stay in default "closed" or "locked" state (there is not "open state available for gate mode) and succesfull use of open, unlock or picklock action on door will just move player to other side of gate. Locking of door can be affected by states "unlockable", "lockable unlocked" and "lockable locked". The level of lock can be function of thieving and construction levels of house owner. However, in case high thieving level locks will be allowed in houses there should be special option displayed by game to visitor without required thieving lvl when they try to picklock such locked door. And it is option to leave (exit) house. Eventually he can be reminded about this option when he try to picklock such door. I know that they can use their house control panel menu for this or home teleport to get out when jailed in someones house. But some players probably never studied all controls even after months of playing...

Compatibility issues:
Two adjacent rooms are actually using shared wall and door with simple formula: If one of walls is solid, both be displayed as solid in normal mode. If both has windows, plain holes are displayed, if both has doorspace, no door is displayed. If one of them has no wall (garden or empty space), windows are displayed as windows, door as closed door etc. Simple and easy. But if we want to add ability to define content of door hotspot, we need to redefine this sharing formula a bit. Seems that basic solution will be to allow building of content only in case that content of adjacent hotspot is "compatible". This means that none or empty hotspots will be compatible with everything. "solid wall" type of content will be compatible with any other "solid wall" content and in case of empty hotspot it will be expanded to it. Other types then "solid wall" (doors and gates) are comaptible only to empty or none hotspots. it means they can be built only on one side and they will be automatically expanded to other side in case of empty hotspot.