I don't think 1.8 items work in creative yet... I would build it on a private server or on singleplayer, which is what myself and a couple of others are doing, because, if you build it on creative, it will most likely be denied for being too small
For now, the server isn't ACTUALLY 1.8, it just works with a 1.8 client (therefore items don't work). You can just submit your map the way you normally would, and the staff/builders will take care of place the barriers.