Experts question: is there any standard for mastering rooms?

Hello, i am going to build a new mixing/mastering room in the future. I am reading here since a long time with a lot of interest. I found very different studio suggestions and solutions for mastering rooms but when i saw Johns works and other professional studios there were conformities in style and size (go by pictures that mostly do not had measuries). So this is a question to you experts who have designed and listened to a few rooms. Are there any studio standards for the style and size of mastering rooms? Or what room size and shape is recommened talking from experiences? I would like to learn more about it cause i started to find the right room at my location. There also will be budget for building a new room if nothing fits into an existing one. Room layouts with measuries and for free standing speakers would be very useful. Thank you very much for any help. Aaron Sommer