Peace be upon you!
What's up bro!! Hope u're doin' good!!
well, turning to our story, I wanna ask, if u do know th system (A_G), cuz it's gonna clarify all thing, if every tone is represented by a letter, it makes it easy, & if u're able to understand it,,it will be easier to use Piano, & fr the black keys, by (A#_G#), & that's repeated with every similar dividends, goin' to the thinner or the coarse voice, (depending on ur choice), & u can also change th musical timbre( according to th developement of ur piano & its brand ,sure) into another musical instrument(such a violin, flute...& so on) , If it's possible I can make sme exp, like givin' sme tones, & u can devin th song ..or conversly, I hear th song & then, I can devin th tones( as I called it: th musical ear), we can also discover melodies frm our own, by followin' our feelings 
..& that depends on hw much u're capable enough to play fuently th piano,, on hw much time u spend with it,, & 'bout experience v course,
It's just a general view...Rap needs "Tones" ! 
& whenever u do so,,, I'll be here !!
Yours very sincerly! .... @ th earliest opportunity incha'Allah