Def floor 1st...no way are you gonna make floor and wall joints align up on opposing walls if you do walls 1st...cud end up with a twisted floor trying to make them meet. Do floor and cover up with sheets!...simple
i ususlly do the walls first then weather i'm done or not, i stop mid afternoon and do the floor so that it is set for the next day and i can carry on with the walls if i need to. saves me time waiting for adhesive to set