Use four feet high panels with plastisol treated tin above the outside side, one block we has perforated tin which lets 90% of the light in but also rain when its windy, inner sides have bars above so they can see each other and the rest of the shed but cant bite each other or get at stuff stored in front, the front of the shed has Yorkshire boarding.I forgot the part of having a horse with anxiety issues - gees they are fun..
More horses in the stables for company - but no, they still want to buck / rear / whiney as loud as they can and kick the sh!t out of the stables...
Oh, and lighting is a topic on its own - need good lighting to avoid spooking the horses due to shadows.
Did you get windows in the concrete panels - or did you simply have none?