Source: http://www.samuco.net/swordedit/sesource.zip
Bug Fixes:
You can save now

I didn't add any new features except for the wall too. Here is how it works:
1) Select some scenery
2) Rotate it to a suitable "wall" position
3) Check the wall tickbox
4) Drag it around to create a wall =D
This took me 1 minute to create (This building is HUGE):



This took me about 20 seconds:

Have fun =D