What kind and size of AC do I need for an enclosed garage workshop?
Lots of variable to consider:  1)  Climate in your area, 2) insulation level of building, number of servers and their size, 3) occasional use or 24/7 (BTC mining? or?) 4) occupied or not.   Google lets their server rooms run as hot a 95 degrees F.    https://www.datacenterknowledge.com/archives/2012/03/23/too-hot-for-humans-but-google-servers-keep-humming So while that's way to hot for ppl, it's OK for servers, at least the kind they use.  Here is a link to a calculator for heat load.        https://www.enviromon.net/advanced-server-btu-calculator/   

Depending upon your climate, you might get by with just moving a lot of air from outside to cool the room. Google runs the Belgium server farm with no chillers.