If you’re thinking about a flock of 12, go big. 6x8 will give you 48 square feet, 4 square feet per bird. That’s usually the recommended space for chickens. I personally would not go smaller. If you plan on a run, recommendation is 10 square feet per chicken. Consider predators-you may want a roof or some type of cover for the run. DLM or some ‘modified’ version is fine. Think about access to cleaning, egg gathering. I had a raised coop in the beginning with a walk in run. I quickly changed over to a larger walk in coop and run, for me it is easier to clean and maintain. All my bedding and poo goes in the compost, I cannot really do DLM as my coop has solid floors, not earth. I do a total clean out twice a year, scoop poop board daily and during winter spot clean shavings and rake some sweet PDZ in as needed to control moisture and smell, top off with some fresh shavings and it works well until the snow is gone and I can do a spring cleaning. Hopefully some folks that do DLM can chime in with their experience 
