To build a terrarium you want to find the container that you wish to use. Most of them are made of glass and wood, or metal. Then you want some gravel or small stones to cover the bottom with, for drainage. Now add a good mixture of planting mix. Now the fun part! Choose the plants you want to use. Be sure you use plants that do not get too big and enjoy a humid environment. Plant them and give them some water. Don’t let your terrarium get too dry, or too wet. Just damp will do.