Well I dont know how to make my own beats in reaper, but I figured out how to import songs from GP and make myself awesome drums for covers.

But here I have a problem. I Am covering a song with temp changes.. How do I change the tempo mid song..?
Peavey ValveKing 212
Ibanez Gio :\
Move the cursor where you want to change the tempo and hold SHIFT + C or go to 'Insert' followed by 'Time Signature/ Tempo Change Marker' and change it from there