Found this awhile back. It can be used for lighthouses, corner towers on castles Source: http://mconstuct.wikia.com/wiki/Circle_Chart Here is an example (I believe we used size 15 for the towers):
Or, You could just open up MS paint, make the canvas the diameter, and make a circle from point to point in thin line, and then zoom in and see the pixels :3 You can make any size with it For example, these wouldnt work for the 2 stone circles we ahev which are 125 and 199 in diameter
and if you want to make spheres you could use this: http://www.minecraftforum.net/topic/26469-perfect-spheres-blueprints-inside/
With dome, Say you have a 15 on layer 1 Your next layer will be a 13 circle then 11 then 9 then 7 and 5 because the edge of a 15 is 5 Bamm you have a dome =]