Multiple Surfaces Skin Scale

I am facing a problem, whenever i have several surfaces or a polysurface which I have to explode before referencing to do some skin work.

Is there a way I can merge several surfaces into one surface

Or

How do you apply a skin definition to small and vast surfaces with preserving scale

or maybe set the unit of skin or a window to a minimum and maximum in real world measurements?

is there a rebuild surface that rebuilds according to dimensions?

an edge every 50cm for example?