Concept sketch for children's fantasy novel

We would like a sketch of a possible illustration to be used as a cover for a children’s fantasy novel Winning bid will also include a price and timeline to fully realize the sketch into a color digital painting. We’d like it to be able to be used for a paperback, so a horizontal piece with most of the interest on the right would be best. 12.3 x 8.75inches, at 300 dpi is what we used for designing last year. The front cover of the space is 5.7 x 8.75, just for layout purposes. Covers that have the sort of ‘feel’ we like are: [login to view URL] [login to view URL] For the scene, we'd like in the lower section of the cover two 12 year old boys, seen from the back, cowering in front of a large, shining golden cloud with a man shaped dark shadow in the middle. On either side, there should be books falling down from shelves - they're being attacked by a ghost in a library. For the back cover part, it could be just more bookshelves - we'll have the jacket copy over it, so little of the action needs to be there. Our target reader age is 8-12, but it will have to appeal to parents as well.