Well, I'm not an expert on terrariums, but I think it looks nice! I don't know if using the river stones on the bottom will change the drainage you get in some way. I used pea gravel for mine and haven't had any issues. I guess just keep an eye on things. Aesthetically, I think the river stones look really nice! Your dessert plants are cute. =) What kind of soil did you use for them? It doesn't look the kind of soil I'd usually associate with dessert plants. Be sure not to overwater those little guys. Did you get a good grade? =)

Thankyou both for your comments, I do appreciate it!

@Keithgh - wow so much knowledge, but so informative! I ideally wanted to add in a piece of wood or an object but with the idea of my school assessments, the plants were able to portray my idea better. I completely agree they will out grow their space very quickly! Before starting the piece I consoled a 'succulent expert' ahah in my eyes she is, as the plants don't usually last long in terrariums, and I decided that once growth becomes quite large I will remove the rest of them, and allow one to take over. Definitely the green one as you suggested. In the store the stones were a good idea, but once I had assembled it I did re think my choices! Thanks alot for your comments, I know where to come for any future ideas :)

@wildhyacinth - It does look nice ahaha and I will have to wait and see a few weeks until my marks have been returned to me! Yes i agree, definitely much easier to keep an eye on things when the container is made of glass. I used 50% perlite and a succulent specific soil from my local garden centre. The perlite just helps with drainage, considering all the plants are succulents/cacti. I watered for the first time yesterday, so lets just wait and see. Already the larger green one has blooming flowers and I can see new shoots, possibly little babies coming out from the sides! So im taking that as a good sign:)

Oooo~~always exciting when you can get a plant to flower. =D

Unfortunately, all the large stones at the bottom really accomplish is the creation of a perched water table. (You can Google that or do a search for it on the Houseplants forum. A gent name Al wrote up an informative article/post regarding such.)

An alternative to Keith's suggestions -- assuming you prefer having more than one plant in that container would be to get rid of the one in the upper left. Plantings generally look better in odd numbers unless one is doing a large mass planting. In place of that plant -- should you remove it -- you could place a "large" rock or piece of wood with some vertical height to it.

Cute setup. :)

I don't have the expertise of these other commenters, but I just wanted to add that I thought it looked nice, and even if the three levels of medium aren't ideal for the plants, I thought it looked cool not distracting :)