You should have a thermometer in the rabbitry. We have a wireless indoor/outdoor thermometer that works well. Use the more expensive lithium batteries because they are much stronger, last longer and aren't sensitive to the cold.
Try to have light colored roofing to deflect heat. On our old rabbitry that had a white corrugated type of roof, using a water hose would bring the temperature down about 10 degrees in a short amount of time.
Having light colored walls helps brighten the rabbitry. We used OSB "chip boards" to line the rabbitry walls and painted them light blue. Using high gloss paint makes it easier to sponge off when the bucks decide they are "P-casso's".