http://www.freecad.com
Search for turbocad
You're after: TCAD_LE_setup_files.zip
This is a free version!
As mentioned elsewhere Google SketchUP is really easy to use for "buildings".
http://sketchup.google.com/#utm_campaign=en&utm_source=en-ha-ww-google&utm_medium=ha&utm_term=sketchup
If it's electronic design (schematic capture) you're after: then TinyCAD is good
http://tinycad.sourceforge.net/
