Very nice pens! Don't fret on the Bobs breakin' necks and killin' themselves on the natural "covey rise" when they're frightened. All my growout pens are 36" tall with metal roofs, and I've raised a bunch of'em ......... and each and every one have hit the ceilings full throttle many, many times .......... bounce off, never say OUCH, and keep on'a truckin'...... Never lost one to the issue yet!
I had one a few weeks ago that was laying in the brooder on its side...even with hatching these little boogers for years, I was certain it was dead. I made a 'gasp' sound when I saw it, to which it jumped up with a look like "what happened??". Silly little birds like to make sure our tickers are working good