looking for ideas for senior project

I want to develop an app for my senior project at my school. I have fallen in love with android development but my teacher doesn't want me doing an app because he said "generally" apps wont fulfill the 5000 lines of code requirement that the senior project requires.I would have to come to him with something solid in order to convince him otherwise, and hes pretty open minded. i will have 1 semester to complete this assignment(jan-may). the project can be anything. it can literally be a copy of something that already exists (someone did a paint program last may) as well as long as I dont steal the code and develop it on my own. Anyone have any ideas for an app I could do?