I think I am sold on the kennel idea. There aren 't any used ones on craigslist yet but the new ones aren't much more.
The shed I am buying used is like this one: https://www.google.com/shopping/product/14253693786341207079?lsf=seller:8740,store:15897478034353444157&prds=oid:10669415372374497446&q=8x10+pop+together+shed&hl=en&ei=0bn4WIChB-aZjwTFvKDIDw&lsft=cm_mmc%3DShopping-_-LIAs-_-D28I-_-100652232&lsft=gclid:Cj0KEQjwuOHHBRDmvsHs8PukyIQBEiQAlEMW0J4_spBDRGgnqHcQAyybx6KBD4qy2W9GGYG5LiRXHpUaApFh8P8HAQ
I'm in the South and it gets HOT. Would have to ad more ventilation definitely. I have pickle buckets was going to use for the nests. I am with you about not attaching it to the walls but have something, like shelving, for it.