Problem with proper drawing size in autocad

I think you're really talking about "limits" rather than "drawing size", which has no meaning in acad-speak. Look up "limits" in the help.
Limits are controlled by the LIMITS command, and if you are getting the same limits on all your drawings it is probably coming from your default drawing template. Change it in the template to what you want and every *new* drawing will be the same. In drawings *already created*, use the LIMITS command to change them to what you want, or, if there are too many to change manually, create a script to do it for you.
I'm no expert on scripts, but someone else might be able to advise on that.

[delete] Thank you very much!
-- Chandler