I used another 3D program that had a useful primitive.
Not just floors and ceilings, but a surface.
Width
Height
Thickness
Elevation
Smoothness (with several choices for rounded edges)
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This let me rough in cabinets, appliances, showers and other things that don't yet have a specific style, or are meant to be in the background. For example designing new kitchen cabinets where the old range hood and center console will remain. I don't want those to have full detail, they're just there for scale.
What's the chance a primitive like this could be added to SH3D?
Not exactly what you want but the Shape Generator plug-in may be useful in some cases. I use it to create almost every model part before I edit and assemble them into a model. In most cases I run it through Blender to add or remove some faces and merge groups. And of course Blender allows to smooth choosen surfaces.
There is also a BasicShapeGenerator plug-in which allows you to create several different basic shapes like pyramid, cross, torus, and more.
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