Autocad Lt is OK, but too expensive for your one time use.
Suggest you go to IMSI site,
www.imsi.com, or
www.turbocad.com, and look at both their Turbocad program and their house design program. Both are excellent and considerably cheaper then AutoCad.
First download the free 2D versions. These are fully functional but don't contain all functions. there are two reasons for this. 1.) You'll get an idea of how the program works, and 2.) they will probably contact you after several weeks and offer to sell you the full version at a further discounted price.
There is also an international turbocad user group. There you can usually get any questions answered by others who use the program for houseplans on a regular basis. You can find a link on the IMSI site.
Hope this helps. I just went throught the same process and ended up with TurboCad Pro, version 6.5, for about $110 shipped. The standard version is even cheaper, and the house plan program is less than that. All three are fully three dimensional where you can actually walk through the house afterwards and see how things look.