Not to scale
I bought these of another breeder, not sure how scientific the exact measurements are. There is a little shelf below the hole the full width of the upper L section and about3mm deep. there are 3 holes (about 5mm in diameter) on front and rear at shelf level for airflow.
I had 3 pairs in the flight, 4 boxes that shape and 4 boxes Mike Fidler's shape and all birds chose the L shaped boxes.
I paid $6 each for mine, figured I couldn't make them for that (although they are a bit rough and ready they did the job).
250mm
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190mm ! I I ! 110mm
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130mm width and also depth (can't draw 3D in machine code.
Yes, I know, taking a picture might have been easier after all. Check your phone

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