Help with a Concrete Wall

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Well I making a map (my sig) and i finished 2 areas on the map, and a few models. I ran into some bumps saying Reached doodad limit but I fixed those. But....then IT came.. "Map file is too big, please try another map."
Im not even half way done and its says that! I have no idea what to do at this point so thats why Im here. Any suggestions will help!