The coop is 4 x 4 inside and the pen is 4 x 8 ( which = 4 x 12 total exterior space ). Following the 4sf per bird rule ... 4 birds.
I used rough sawn lumber and plywood for the exterior, standard (cheap) plywood for the floor (1/2 sheet) and osb for the roof panels. If you use metal roofing or corregated roof panels you could omit the osb and skip sheet it (to save a few pennies). Construction glue and screws work great. I use stain instead of paint just because I don't have to prime before staining.