For this type of project, you can zoom in on the traditions of a specific tribe, or you could find a theme (tricksters, ghosts, warriors, etc.) to bring together stories from different tribal traditions.
Research Tip: The best place to start is with the different Native American books at the Freebookapalooza. You can then use Wikipedia to get important background information about the tribal tradition you want to study. There are also many Native American units here at the UnTextbook that you can browse and explore.
Note: It is important to work with reliable sources because of the "fakelore" online, like the so-called "Native American" or "Cherokee" story of the two wolves; if you are unsure about good sources to work with, let me know, and I will be glad to help!