Wall dimensions

[mountaineer]

Ok, this might be a very basic question but.... here goes.

I need my foundation to be 1.5" less on all four sides than my main floor perimeter dimensions to accommodate siding over the top section of the foundation wall.  I can't just change the dimensions because it doesn't change equally on all four sides.

I know there is a way to add a -dimension but I haven't had success.  Also, if I push the wall manually it only allows me to move in 1" increments.  Is there a way to push the wall just 1/2"?  Any suggestions would be great.  Thanks in advance for any input.