I'm in South Texas, near San Antonio, so heating isn't really a concern. There are a few days a year when it's really needed but a 20 degree rise will make it comfortable.
I did 16' eave height on the last shop, I'll probably do the same here. I kind of have to in order to have the mezzanine, unless I do a pretty steep pitch. My forklift goes 16' so, I can use all the vertical space.
I don't need a floor drain, I'd much rather wash stuff outside. I don't want the mess inside. I'm planning to either extend the roof out 15 - 20 feet on the sides of add lean-tos. I'd prefer the roof extension, I think it looks better.
I oriented the last shop to take advantage of prevailing winds with 2 roll-up doors across from each other to get good cross flow, it works really well to keep it cooler in the summer. I'll do the same here, only I'll add a 3rd roll-up door on this one. I rented a shop in Houston that was 50x75 and had 4 doors, it was nice for ventilation since that building wasn't insulated but, I only used 3 of them for access. With insulation and an AC, 3 will be fine.