Here are my suggestions,
At one point gliders did not exist, only birds and seeds possessed the ability to glide. Someone had to make the first glider for a human and had no option to purchase it... so I think your desire to make your own is totally reasonable and high adventure.
However, take into consideration that you will need the time and money to build your first glider and then the time and money to improve your design. Likely, as you have already stated, you can't afford a proper set-up so you'll be purchasing less than adequate materials. This could mean that your first glider(s) will break. That's OK as long as you expect this as a strong possibility and attempt to protect yourself from physical harm.
I don't think there's anything wrong with saving money, inventing, creating, or taking risk, but I think you should be in contact with someone who knows what they are doing to help you get familiar with good building practices. Find a local club to hang out with and volunteer to help them set up their rigs. I imagine that you could learn a lot of information first-hand on a few days out with a group. Besides, this would be a great group to be in contact with in case you decided to buy a used glider.
My suggestion would be to buy used or rent for this summer season until you have the basics down. Then try to make your own glider over the winter after you've learned what a quality rig should feel like.