That's right. Underdeck drainage system is another way to solve the problem. The pros of underdeck drainage system are the installation is easier than roof deck and the cost is cheaper. I think if you want to make your project easier and save your money, underdeck drainage system is a solution. However, I think there are some problems of underdeck drainage system that you should consider. When you install an underdeck drainage system, you have to make a smoothly graded surface that slopes toward the courtyard. Otherwise, more and more water will accumulate to become a pond under your deck. Then, it will benefit for vegetation and algae growth. Also, the life of your decking material may be suffered. Therefore, although it is easier to install a underdeck drainage system than roof deck, yet make sure to have a smooth surface and the slope. Hope I can help.