I don't have any particular source but my preference is for a thinner, tighter weave with a significant amount of polyester in the cloth. With a tight weave it will block the sun and wind and still breath. The poly helps it wear a long time and prevents catastrophic tears. Rip-stop is good if you go 100% cotton but a bit of poly works as well and helps the cloth dry faster.

If you treat a tight weave cotton-blend cloth with a durable water repellent, DWR, from Nikwax or similar it will shed a good bit of rain without feeling stiff or scratchy, and it will still breath. There are some very tightly woven cotton cloths that are virtually waterproof because the threads swell as they get damp but products that incorporate such specialized cloth are pricey. IMO you can do about as well for less.

Online shops like Duluth Trading and LLBean are good but you can often find suitable shirts at Sears, Target, discount stores and second-hand shops. Often the best buy is a $17 dress shirt. Buy them a little loose and you can wear it as a light jacket to block the wind and wear a poly thermal or Henley and tee underneath. With nothing underneath the thin but tight cloth keeps the sun and bugs off and it can be worn sleeves down and buttoned up without overheating.