Can someone please explain to me what purpose the shape of an item has? I've seen them used on different maps, but I can't figure it out. If you don't know what I'm talking about, it's in the item's options I believe. You can make it a box or a cylinder. Also what are the safe/kill zones and the difference between soft and regular? Is it just the two ends of the boundaries?
Some items have an area that they affect (Teleporters, Hills, etc) you can change the shape to better suit your needs for instance sometimes its easier depending on your map arrangement for the area to be a box shape instead of sphere. Safe zones means every area inside the zone is legal to play in anything outside is not. Regular Safe zones will kill you instantly if outside its defined area. Soft safe zones will give you the "Return to Battlefield" warning and 10 seconds before they off you.
Great answer here. Just to throw in something, it can sometimes be a little clumsy working with circular hills and objectives (they sometimes tend to allow little hiding places or not hitting/hitting areas you want/don't want it to), and the same with the square objectives. Depending on your map, though, one or the other you'll find is usually more desirable.
I'm unusure that the object size property has a direct influence on gameplay. I've noticed this is on one way shields, and it doesn't appear to affect them at all. I spent a good few hours playing with them yesterday to create an enery bridge but I can't for the love of god prevent bouncing using the object size parameters. So, it appears, this doesnt always affect things.
Maybe have the shield doors positioned so the players will fall through, but place thin 2 x 1 or 2 x 2 blocks underneath the shields if you can.