A small greatcoat requires about 3 yards (12 quarters) of coating weight wool, 2 yards (4 quarters) wool flannel to line the body, 1 1/2 yards (6 quarters) unbleached linen for slipability in the sleeves & cape & finally a stirp (~1/2 yard or 2 quarters) of buckram interfacing for stability. Some woolens have a grain that will require more yardage to keep the grain running in the correct direction. All yardages are only suggestions & are at your discretion.
Notions required include a spool of 35/2 linen thread or 50/3 linen thread to match & 1 to 2 spools silk buttonhole twist or quilters thread for buttonholes. If you use buttons just on the front & skirts 12, 1″ buttons is all you need. If you decide to add buttons to the cuffs add another 6, 1″ buttons. If you decide to add buttons to the pockets as well add another 6, 1″ buttons. And finally, you can add a second, 1″ button to each skirt so that the greatcoat can have anywhere from 12 to 26, 1″ buttons.