¿how can I make a ramp in the shape of snail?

 From:  diego
The width of the ramp I want to make has 0.5m in the beginning and 4.5m at the top, the height es 3.4m. other thing is that the beginning is 15m frome the center to the out edges and the end is 11.8m from te center to de edges. I wish someone could help me.