Wii fire code violation?!

How big is the house you are trying to build?

It didn't list the size, but I tried to measure it myself using the grid's squares and it's about 8 x 15.

Do you only have this with this particular game save / lot or do you have that all the time?

Well, this is the first time I'm trying to build my own house rather than buy an already-built house.

Can you try it on another lot or with another save please?

I tried it on another save and it worked, but there were a couple variables that may or may not have contributed to it working.

First of all, it wasn't the same house.  Since you had asked me to try it on a different save, I just started a new game and immediately went to buy the house.  Since I didn't take the time to get a job or earn money, I couldn't afford the same house that's giving me the problem.

Second of all, in the save that's giving me issues, I ran out of free space because prior to attempting to build a house on an empty lot, I lived in the mansion-style house.  In that house, there is no free space available probably due to the size of the house and the amount of furniture in it.  Even after selling some of the furniture in that house, though, there was STILL no free space available.  That was why I wanted to move in the first place.  Therefore, it might be a problem from the free space issue with the other house that's somehow affecting me building a house in an empty lot as well.  In the new save that I started, I obviously didn't live ANYWHERE before I attempted to build the house on the empty lot, so I never had a free space issue before attempting to do so.

I hope this all makes sense.  I'm not sure if any of that makes a difference or not, but I just wanted to state those variables just in case!

Try putting a fire alarm in every room of your house. Once done with that, remove all of the alarms (unless you wish to keep them of course). If this doesn't work, go back to playing mode then switch back. 

Unfortunately that sounds more and more like a corrupted save file to me. Do you have the possibility to move your family out and start with them in another neighbourhood?

Sorry it took so long to get back to you, but I thought the problem was fixed.  Since you suggested that the file itself might be corrupt, I decided to start an entirely new file with a new family.  Everything was going fine.  I built the house that I wanted, set everything up, and by the time I was done, only about a sliver of the free space bar was filled up.  Then, my Sim had a baby, so all I needed to add in the house was a child's bed.  Now all of a sudden when I go to buy a bed, the free space bar is completely filled up.  I'm starting to get quite frustrated.