I am 5 feet 7 inches tall and all my indoor layouts have been 48 inches high.
I built a large portable layout for a show once that was 36 inches high so kids could see it.
I have nine grandchildren and if they want to look at the layout they stand on these otherwise I give them a box of figures and they play under the layout (kids have great imaginations they don't need a fully detailed layout to have fun) or with this I built it myself 10 years ago which is 16 inches high. Roo.