Very basic. There are a lot of advanced things that I would recommend doing such as having an item be unlimited so you can have less copies in the selection area, but use as many as you want in the creation area. Even if you wanted to do something more simple you could have made multiple copies like 100's of each and placed them over top of each other. That way when someone dragged one into position there was just another one waiting for them.
You should have every item facing left and right equally. You have an over abundance of facing to the left, but hardly anything facing to the right. The selection area is way too big and the creation area is way too small. The white areas in between the sections gives it an unfinished and unpolished look.
It would have been better with some background music or even a selection menu for choosing background music. Think of your common Madness video/game songs and go from there.