starting a new ss

i looking into starting a ss. i found some land that gets about 13k cars daily, has a pop around 30k +. i am trying to figure out how much this location can gross a year. compeitiion is a gas station that is a tunnel car wash, nearest ss is about 8mi +/- away. looking to put i 4 ss bays with 1 iba. vaccums, floor mat cleaner etc. what is a reasonable amount of money each bay will bring in. How do most people go about putting a proforma together. any info will be much appreciated.