if my roommate charged me for toilet paper they picked out I would want to talk to them about the brand they go for and other details, at which point a lot of the overhead is back isn't it?

That's sort of the tradeoff, though. You get the convenience of having tp show up without having to to through the steps of shopping for it. Except in extreme cases, it seems likely your roommate will pick something that is effectively a commodity at a reasonable price. If you want granular control over brand, features, and pricing, you'll have to pay for it in time and/or money.