A cactus terrarium sounds like a nice idea. Put a bunch of your favourite cacti together in a glass container along with some props and live happily ever after. The problem is that cacti aren't really compatible with terrariums in their traditional form.
A terrarium is a self-contained ecosystem that keeps moisture in, humidity up and airflow down. None of these are attractive to cacti. Cacti like good drainage, low humidity and good airflow.
If you plant cacti and succulents in an ordinary sealed terrarium, they'll probably last a couple of months but will very likely not liver any longer.
But it would still be really cool to have a terrarium with cacti and succulents. Your desert in a glass. To achieve this, I suggest breaking some terrarium rules and following these guidelines.
No, it's not quite a terrarium anymore, but this will do two things for your precious cacti. Firstly, it will decrease the humidity by allowing excess water to evaporate. Secondly, it will improve the airflow substantially which cacti enjoy.
By going for a wider bowl, you're going the extra mile to improve airflow and reduce humidity. Straight sides prevent distortion.