Roku

I just bought a roku for my tv. This is a tv transmitter so on the tv mount I need to build a shelf that sits underneath the tv. The tv I have has a DVD player built into it so I am going to try to make a shelf that can be a place for both the roku and DVDs but I was already worried about the weight of the tv mount without the additional shelf so I need to figure out a way to include this shelf and keep in at a reasonable weight for hanging on a wall.