My nestboxes are entirely internal to coop and just above floor height so I hinge the lid up for access. I think if I went external I'd give most consideration to making sure rain can't get into the box, so I think having access door hinge down would provide the best weatherproofing.
As far as a communal or split box, I've had it both ways and I don't know if the chickens have a strong preference. I guess I like the look of the individual stalls, but depending on how many hens you need to accommodate, a communal box might be better. Recommended is about 1 box for 4 hens, so if you have 8, 2 stalls should be fine, but 9 or 10 would probably be able to fit 3 to a communal box if needed.
As far as a communal or split box, I've had it both ways and I don't know if the chickens have a strong preference. I guess I like the look of the individual stalls, but depending on how many hens you need to accommodate, a communal box might be better. Recommended is about 1 box for 4 hens, so if you have 8, 2 stalls should be fine, but 9 or 10 would probably be able to fit 3 to a communal box if needed.