Well...it may be possible, but it certainly sounds like it could be a complicated project. There are so many possible types of things that can be on a drawing sheet, and some of those things do not have a convenient or accurate way of determining the space they take up on the sheet. And I don't know of any pre-existing method for finding specifically sized open spaces on a drawing sheet. Some things have bounds, borders, or RangeBox type specs, but they can sometimes be misleading/inaccurate. And somethings, like Revision Tags, do no even have API support, so you may not even be able to find them by code, let alone get size/shape/position data from them. It certainly sounds like it could be a nice tool to have available for drawing automation purposes though. Might even make a good post for the Inventor Ideas forum, requesting that a tool like this be made available through iLogic or the API. Otherwise you simply need to have very intimate knowledge of your drawings, and everything that you put into them.
Wesley Crihfield

(Not an Autodesk Employee)