I have runners and I designed a house that is four feet high. Reasons:
Runners can stand up to 34" tall (the tallest I have read about). Many are between two feet and 30 inches tall.
I use loads of bedding as insulation, for comfort, and for relative cleanliness (I fluff the bedding - it dehydrates the poop rather quickly). By loads, I mean a foot and a half or so. 4 - 1.5 = 2.5
Plywood comes in 4' wide sheets.
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The door is two feet high.
My tallest runner turned out to be about two feet tall. But I have no drakes right now. Many runners are not show quality, which are the very tall birds, though.
I also installed last fall a plexiglass drop ceiling to help keep more heat in during cold weather. It also helps keep rain from pouring in during ripping storms. It's in three sections so I can slide one section over and let more air in during the heat of summer.