It's not that noobish of a question, the BPM cube has never been duplicated in SM before.
Anyways, the cube is going to have to be a Sprite (unless you decide to cheat and use a 3D cube, which is a much easier option), with the main problem being that you can't really control the delay times of the sprite dynamically (to the BPM). The code I use in dubaiOne to get the bpm (on ScreenGameplay though) is:
Code:
local songBPS = GAMESTATE:GetSongBPS();
songBPS = songBPS * 60; -- beats per minute