There's an easier way to makes plain circles and spheres.
For circles, go to MS Paint and zoom to 800%. Then, zelect the circle tool and make sure it is on the lowest thickness. Draw a circle with the desired diameter (you can see paint telling you the height and width in the bottom right corner). Now copy each pixel into minecraft as a block, and you have your circle.
For a sphere, go to
http://www.plotz.co.uk/plotz.php and put in the diameter you want. It makes a sphere for you, so just copy it into Minecraft.
For your other shapes, you probably will have to use binvox, but if you don't want to buy Sketch-Up Pro then you can use a free 3D modeling software called blender. It might be a little bit harder to use, but it is free and its .obj files should work just fine for our purposes. Alternatively, you could search for a free 3D model of the polygon you want in .obj format, and binvox that, but I cannot guaruntee any results there.
Hope this helped!