Google sketchup is a google product that was designed as a 3-D modeling program. I will show you how to use it to make a halfpipe
This is the step shows what the base of the ramp will be
2: Making it 3D, Putting Some Life Into it
here is what to do to make it 3-D. You will use the push/pull tool and the curve tool.
3: Delete the Lines
there should be one vertical line on each side, use the erase tool to delete them if something bad happens stop and go to edit>undo erase
This is how to make the pipe that is on the edge.
5: Copy and Paste
Make the other half, this step uses the rotate tool, line draw, and move tool.
6: Finishing Touches
Finish it up! you will use the paint tool, and the mouse tool.