new to the site

Helloo and welcome.
The main thing you need to think about is the size of the run - and for 12 hens who will be in there full time you need to look at a run that has at least 24 square meters of run space. Any less and you run the risk of the birds becoming bored and start bullying. Also too small and the ground will quickly become stagnant and lead to illnesses. They will need several feeders in there and drinkers plus a dust bath area.
The coop will need 12 inches of perching space per bird and should have 4 nest boxes.

 ... and once you, as the responsible chicken owner you are, have provided them with spacious and comfortable accommodation, they will proceed to fight to the death to squeeze into the same square inch that the other chicken is in.

Think toddler with feathers.

Oh, welcome to chook-a-holics. Nice to meet you.