The issue of maintenance and of acceptable housing conditions are totally separate. You are mixing them together to justify your position that you deserve maintenance. You deserve maintenance if you have the child the majority of the time regardless of whether her father lives in a palace or in a shack.
It sounds to me like you are upset at him saying you have 'shared custody' when you actually have the child more than 50% of the time. And that you are upset that he is saying it in order to avoid paying maintenance. If what I've said is correct, then whether he is living in a mansion or a shared one bedroom flat is irrelevant. It is an issue of TIME not 'housing conditions'. If you feel you are due child maintenance based on the fact that you have her five nights to his two, then take legal steps to get it. Just because he says it's 'joint custody' doesn't mean that the authorities will agree with him.
As far as WHERE he 'houses' the child when she is with him, he can house her wherever he can afford to as long as it is clean and safe. A camp bed in his bedroom in a shared flat is clean and safe. Reverse the situation and ask yourself if that was the best you could provide for her, would you think it right that he criticize you? Of course not.