I'm new using AutoCAD 2004, and I wanted to draw part of a building, but it seems like the model space is too small to fit the drawing. What could I do?
What you are saying can not be true. Modelspace is basically infinite. Did you mean Layout space with a viewport? Or could you mean it would not fit in a defined viewport in modelspace?
"Everybody is ignorant, only on different subjects." — Will Rogers
Draw in full scale in model space.
Zoom in or out to facilitate drawing.
In paper space, put your title block and open viewports to the objects in model space.
You may have to reset your limits to view all of your geometry. It's been awhile since I've used autocad, but I believe "zoom extents" effectively resizes the limits. Or you can issue the limits command to resize them. The limits command does not effect how big the geometry can get it just changes the view limits.