trying to make multiple configurations of simple rectangle for varying sizes

Hello again all,

I'm not sure of the basic steps for making multiple configurations of the same part or how to achieve this instead of having to make a new .sldprt for each size (haven't really used the configuration tab in SW yet).  What I'm trying to do is make several different overall size steel plates with varying thickness for use in an assembly but I believe I could just sketch out a rectangle and add a new configuration that would allow me to key in the overalls for each?  As far as the extrusion for the thickness, not sure when this would be done.  Just looking for a basic step procedure.  Can I just start a new part and sketch a rectangle on the right plane without specifying the overalls, then from that sketch add a current derived configuration from current configuration and within that configuration specify the size and extrude it?  I tried this and it doesn't allow me to edit the overall rectangle sizes.  Appreciate any input as to what I'm doing wrong.  I'm attaching 2 screenshots for reference.  Thanks!

SolidworksSketching