There is no hard, and fast rule as to what height a layout should be, it's whatever suits your requirements, but don't forget to take into account that you have to reach across to which ever the width is going to be. I suffer from sciatica, so for the sake of comfort, and being a shorty at 5 foot 7inch my baseboards are 2 foot wide, so the comfortable height for me is 40 inch. All my point motors are top mounted, and diguised under lineside buildings. The wiring looms, connectors, solder tags,and rail wire droppers all come out to the operators side of the layout instead of underneath .

John,

For me there is nothing like watching a layout where the trains are at eye level -  this present a problem in that if you are viewing standing up you will not be able to have a layout with any meaningful width.   I  compromised and have mine at a level where the track is approx eye level when sitting down.