Building Block This first option lets you pick a building block. Since these building blocks stack and can move around, this piece can be used at the top, bottom or in the middle of the additional modules you select, if any. Should you opt for no additional modules, this building block includes the closure top necessary to have a finished unit, hence these building blocks cost more than the additional modules. Make sense? If not, call us. 888.467.6278 will land you an expert.