Default Asks to instal supersu

I was on rooted stock rom and decided to change my rom for the first time, i downloaded RGUI by gh.rohit , booted to recovery then cleared cache, data, system, dalvik cache, and then flashed the zip file, everything was fine then after completion when i pressed to reboot system, a pop up message came asking me to install supersu,i swiped to instal, and then my phone is in bootloop, currently going back to stock, but i want to instal RGUI , can anyone tell me where i went wrong?
Phone history:
Nokia 3310
Sony Ericson 580i
Nokia N72
Nokia N73
LG Optimus Black p970
Samsung galaxy s i9100
Apple iphone 4s
Samsung galaxy sIII
Apple iphone 5
LG G2 D802