Hi Astrodude, i too am planning to convert my shed/ garage into an obsy.
It unfortunatly has a concrete base i have to cut through first, oh well
My point in replying to your post is that the people i have talked to on the subject of pillar foundation blocks is that a 1m x 1m x 1m block is probably the minimum for stability and vibration dampening.
I am sure you will get all the information you need here to build a top class observatory, their are some pretty talented telescope and observatory builders here.
All the best mate...........
Tony.......