What you suggest could be done. You'd just have set up your code to execute as SketchUp loads, rather than giving the user the choice. BUT this would be very restrictive ! With your concept, every time a user opened SketchUp it'd run your Plugin to make a room ? What's so bad about having it like 99.9% of tools, which run off a menu entry [or toolbar or context-menu] ? You have given a limited description of your tool, but I suspect that you don't really want to do what you have so far said...