You do not have a complete question. I do not know the dimensions of the half pipe nor the deck. I will assign letters to these. Hopefully that will help.
R = radius of the pipe
L = length of the pipe
W = width of deck
l = length of deck
area of the half pipe is the circumference of the pipe times its length.
Area-half-pipe = pi * R * L
Area of the deck = W * l
If the two decks have the same dimensions then double this number and add them up.
If the half-pipe has a flat cover its area is 2*R*L