I have to be honest with you and say that, while obviously symbolism is a key literary device used by Poe to great success in this wonderful story, I don't think that the seven rooms can be related to the seven deadly sins. What I think they do represent is the passing of time and the different stages of life. Seven is a key number - there are seven days in a week, and then we also have the seven stages of man. To my mind, at least, this symbolic meaning of the seven rooms is more important and fitting to the story than arguing that they represent the seven deadly sins. Remember the context of the story - we are presented with Prince Prospero and his revellers trying to lock out the Read Death, which could be said to represent death itself. They are trying to cheat time and death and live riotously for all time. The setting of this final party is richly symbolic, and thus each room could be said to represent a different stage of life rather than a sin. Of course, the final room, where Prospero finally meets his intruder, represents death, as is enforced by the black ebony clock, that represents the passing of time and the approaching final hour.
However, having said that - if you can argue your case convincingly, you go for it! That is one of the joys of Literature - if you can make what you think sound credible, there is no reason to say that you cannot prove that I am wrong and the symbolism of the rooms indicates the seven deadly sins.
each of the colors of the rooms represent a seven deadly sin. like the blue room would represent pride and the black room would represent sloth. you could also relate them to the seven stages of life. or you could combine both the seven deadly sins and the seven stages of life to the colors of the room. pride and birth would go with blue. sloth and death would go with black.