I am sorry if MagNet didn't put or make the poster model so original credits to who did it.O.k to make a menu for u mingie bags first you go to youre steam folder and then steamApps then sourcemods then gmod 9 now that you are there you should go to settings then to menu props and then make a text file then type or click previous one and type
"MENU NAME U WANT"
"NAME OF MODEL U WANT" "models/posters/post01.mdl"
That above is the spawn menu replace NAME OF... with a name u want for it. Make sure you click save when you are done go to gmod and look for it under the scroll down you should see MENU NAME U WANT and then click that and then go to It and click it done sorry if this is an unclear small tut.