Here's some basic code to get you started on your own UDK top down shooter. This isn't the code you normally get while searching for this kind of thing and if you run through the normal tutorials then try this you'll notice a huge difference between the methods. For starters this camera doesn't tilt while you're moving, and your reticle is free roaming as opposed to invisible or non existent all together.
I take no credit for these, they're readily available around the net as is if you know how to look for them, it's where I started, and I've since re-done them all but I keep backups just in case or for reference.
here's the link
They're already in different classes
create a folder in your udk>development>src folder called topdown and inside that folder make another folder called classes and stick these in there
in udk once you start / restart it it'll be an available gametype, after you select it you should be able to just play and you'll get a top down view, no enemies or anything I won't do it all for you, but it's a great start for newbies.
You'll find that unlike most of the top down tuts out there which don't give you any real "shooter" info this comes with actual crosshairs to play with, and you can easily setup a kismet to give your player a gun, because it's almost always recommended you not give the player a starting inventory. Just connect the out of player spawned to the in of give inventory and set the player as the target of that.