2 parts to this question.
What is the biggest home observatory:
1. Money can buy
2. In the world
When I mean "home", I mean on a private property ie. backyard, and owned solely by the property owner.
If any one of the forumites actually think they own the biggest home observatory, then show us your pics to earn bragging rights.
EDIT: Show us your pics anyway, regardless of the size of the observatory. Home observatories are so COOL.