I'd like to notify >>486 in the demands thread that Marbuel doesn't seem to exist; granted, any imaginable entity has some sort of existence, but Marbuel seems to be an invention of the chart creator. And the seal for Gamigin would be one I was sure would be used for Glasya-Labolas, so I wouldn't use that chart at all.

If you wanted to try non-demonic entities, Gabriel should be good for help with art and architecture, and I'd expect him to have an existence strong enough that you don't need to be a master summoner to get him to help you.