How much will my SSI Decrease when I roomate in with my friends?

One of my friends makes 10$ an hour, up to 1200 a month, the other only makes 8.25$ an hour, and gets roughly 500-800 a month. I currently am in my own apartment, and we are moving out of the ones we seperatly live in, and into a 3 bedroom together that costs 799$ a month. I need to know how much my SSI is going to decrease, considering one of the roomates makes almost twice what I make I'm very sure it's going to go down, and he needs to be sure that I can continue to support myself without having to pick up the slack. I am a very self dependant person and have rented my own apartment for the last 3 years, before that I roomed in with the same roomate who makes 500-800$ a month without it decreasing, only it was a 1 Bedroom not a 3, and the SSI I recieved did not go down. I am going to have to report this once August 1st hits, and need to have at least an estimate for my friends of how much I am going to have to put forth, considering I have no idea how badly his 1200 a month might sack my SSI. I pretty much know from previous experiences that the other roomate doesn't effect how much I get very much if at all as when I reported that there was no decrease, however 1200 a month out of 799 is ALOT, which I'm worried will nerf my SSI into the lower 200 or 300s, which is how much I am saving up monthly for a used car.