Box is one of the default objects for Sweet Home 3D. When you search for "box" in the catalog it should be one of the first few in the results.
Other default shapes are Cylinder, Triangle, and Sphere.

There is also a plugin to create your own 8-point shape: https://sweethome3d.com/support/forum/v ... hread,6600

And there's a Basic Shapes Plugin to create shapes like a pyramid, torus, etc. but the URL to that one seems to be missing in the plugins list.