A Chattri is "a domed kiosk supported on pillars."1
Chattris can be found at three locations in Humayun's Garden Tomb.
There is a pair of chattris in what would be good positions for lookout posts on top of the West Gate's facade that greets tourists as they approach the garden tomb.
There is a set of four blue-domed chattris on top of the Barber's Tomb, one at each corner.
Humayun's Tomb has eight blue-domed chattris, a pair on each pishtaq. Four larger chattris sit on the roof directly above the ancillary chambers. All of the chattris on top of Humayun's Tomb are functional pavilions. The blue-domed chattris can be accessed by staircases that are inside of roof pavilions that are located within the top of each pishtaq.
1. Catherine Asher, The Architecture of Mughal India (Cambridge: Cambridge University Press, 1992), xxv.
Burton-Page, John. Indian Islamic Architecture: Forms and Typologies, Sites and Monuments. Edited by Michell George. Leiden; Boston: Brill, 2008, 74-5.