If it is to be a one time operation, just rent a mower with a bag. You could hire it done one time considering the time and money in materials you will spend making a bagging system yourself. Your safety has got to be worth something.
OTOH, if you just HAVE to make one, I suggest that you go look at one in the store. That will give you an idea as to how it should be done. Look at both the materials and the construction methods.