Here is good books in levels:
Beginner: Out of My mind, The mixed up files of Mrs. Basil E. Frankweiler, and Pippi Longstocking
Regular: Percy Jackson, Fantastic Beasts and where to find them, chomp, and hoot.
Advanced: Harry Potter (1-7, though 4-7 are hardest), Where the mountain meets the moon, Starry river of the sky, and when the sea turned to silver