IMO, a few factors you need to consider
1. The purpose/usage of the backyard Vs. the practicality of the material
2. The security
3. Source of light & air flow
4. Cost Vs. Budget
5. Maintenance

If this backyard does not required any practical function, I think tempered glass will be very nice if the budget can afford it. Bear in mind that it is calculated based on sq.ft. It will give you natural light to your backyard, and you can install some LED down-lights as well. Maintenance wise, you will see a thin layer of dust sometimes (just imagine you didn't wash your car for weeks, and what you will see on your wind-screen ), hence you need to clean it from time to time.

If this is similar to the glass roof for car porch, I was quoted between RM45-50 psf with 10mm thick tempered glass, hollow frame.