i may be 12, but i have a freind in the armed responce police, and he was accepted for being a sniper a while ago, i was just getting into airsoft at the time, so he let me watch how he makes a gun ghillie, pretty much what you do is get either a scrim net or hessian bag which has been cut to your guns size with holes for any optics you may have, if your doing a sniper rifle, leave either room for the bolt or cut the bag/net short there so you can get your hand under to the bolt easilly... after you had made one to fit your gun get dark coloured and camofluage meterials ad cut them messily (but dont go crazy, your fingers do help during a skirmish) into random shapes and sizes and randomly stick it on, but dont overflow any perticular area, as hessian/scrim is a nice nattural colours unlessed its been died, also another good idea is to put elastic on parts of the gun like on top of the scope and any over unopperational parts during firing... you can then use them to attach foliage and over things like that, make sure the barrel has a good 2cm clearence of the hessian/scrim becuase it can easily redirect the BB...