Making a simple 3D shape

[Terryhoc]

New user. I'm experimenting with a custom-designed staircase. Steps have proved to be easy but bottom and top steps require a special shape. I can 3D model these using walls and export but this gives me a 3D model with sides only. (No top and bottom.)How can I achieve a simple 3D model with all sides, top and bottom? (Like a solid object)

[Puybaret]

Simple shapes can be built with Shape generator plug-in available here.