When I was building my armory, I bought everything that was on the building list. However, for whatever reason, the walls didn't show up. They eventually did show up on the list, and I built them, but I have to say that I rather liked the look of an armory without walls. The two doors inside of your home, instead of taking you into the armory, took you outside to Skyrim. On the outside, it looked like you had a patio. There wasn't any furniture, nor the option to add furniture, but it was an open, outdoor stone patio with a porch covering it from above. The porch was still fully functional, so I could go up to the porch and still have the patio underneath. I really liked the look of it.

I'm not sure if it was a glitch. It may have been, since the walls never appeared on my list, but could you deliberately leave a house unfinished to get the effect? Without the ability to place furniture, an outdoor patio doesn't look very impressive, but maybe you could throw some pelts down there. I think, in most instances, items dropped in the open world tend to stay there. I mean, the roads near Riften are littered with the swords of fallen bandits.

Items I have placed outside have stayed there for the entire game (note, I have not tried this in a city or around large groups of NPCs. So, it stands to reason that anything you place on your patio will be there.

Until you trigger the script that builds the next part of your house on the area where you placed stuff.

Well I arranged some dead hawks on the Proudspore patio and the clean up code got rid of them on the next visit, I have not tried the new homes yet.

I can't answer your question about whether or not placed items will clean up after a while, but I do intend to deliberately have a home or two unfinished.

After reading that each home will look pratically the same when each are completely done (with location being the only difference other than the specific upgrades like the Fish Hatchery thing), I thought that I'd only have one house completely done up and furnished, with the other two differing however I can.

The only problem is I need to decide which of the homes I would prefer to have as my 'biggest'. That is purely down to location. I haven't been online much since release, but I'm trying to find images of each house and/or the exact location of each plot, so I can perhaps have the decision made before I purchase Hearthfire.