if your floor is made of sprites giving a graphical representation of a slope then you can give the sprite a variable based on that angle...
so if your slope is 45 degrees set the variable to 45...
then you can set the players angle based on that variable when he is stood on it..
remembering that 0 degrees is to the right,imagine East on a compass so 45 degrees would be South East on a compass, you would have to do a calculation to get the correct angle...