I am supposed to be making an engagement cake. I found an idea on here with a two layered cake with the ring box sitting on top. Question is how do you make it????

I made one of these once - it was great fun. I made the box and lid separately out of RKTs then iced them with RI and covered them in fondant. I put the lid on the box with two skewers cut to size and set into the back top edge of the box at an angle. I then placed the lid onto the skewers in an open position. It was very stable. Of course, if you could put an isomalt gem in for the stone instead of a gumpaste one, it would look a whole lot better! Here's the link to my picture:
http://cakecentral.com/gallery/2021565