Step 8: "Painting" the Structure
I have found that, indoors, spiders don't like raw cement. If you paint the interior with house paint, the spiders come and you have cobwebs to deal with. I just mix cement (gray or white cement) with powdered pigments (sold for tinting cement) and use that instead of paint. It lasts a lot longer and is a lot cheaper than regular paint.
I hate elastomeric roof sealers. Once you paint your roof with elastomeric sealer you can never get cement to stick to the roof again and you are trapped into potential elastomeric nightmares over time. Instead, I use a cement base sealer called Thoroseal. It never peals or blisters, but does weather away gradually from sun and rain. The Thoroseal is expensive. To protect it, I then put a coat of colored cement over it, like paint. The colored cement is a cheap, sacrificial layer. When I see white Thoroseal showing through it, I know it is time to apply more colored cement.
I use broom heads as brushes to paint with. For the final touches, I sometimes splatter on more diluted solutions to get mottled color effects.
For more painting-with-cement info see: http://www.instructables.com/id/Painting-with-Colored-Cement