Since this is a creative assignment, it is not as specific as other projects. However this could be fun. My advice is to try some things, and then save your work, and then try other things, so if you don't like your changes, you can `roll back' to a previous version of your ideas.
Music is in quotation marks because some of may not be able to write a simple tune, and you will not be penalized for that. Consider using sound effects instead of music: bird sounds or sirens can be made with several loops one after the other.
This will be more practice with looping using the following BASIC statements:
FOR... NEXT, COLOR, LINE, CIRCLE, PAINT; SOUND, GOSUB ...RETURN
For the ear to perceive constant distances between notes, the frequencies perceived be in constant ratio. That together with the fact that two notes with the frequency doubled sound `the same,' allows us to conclude that each note has a frequency that is 2^(1/12) times the frequency of the previous note.
COLOR 10, 1 ' corco foreground, background
FOR x = 200 TO 300 STEP 2
GOSUB DrawCircle: y = (x - 200) ^ 2 / 30
GOSUB EraseCircle: SOUND 500, .3
NEXT BEEP
FOR xX = 300 TO 200 STEP -2
GOSUB DrawCircle: x = 600 - xX y = (xX - 200) ^ 2 / 30
GOSUB EraseCircle: SOUND 1900, .3
NEXT
END