I personally would not use a glass top but if used don't cover more than half of the screen top. Most tree frogs like ventilation. Providing live plants in the substrate will help with humidity, as well as sphagnum moss for substrate, which retains a lot of moisture. If you create a living terrarium with a gravel or hydroballs drainage layer the water in this may raise the humidity as water collects. I've found coir and spraying the tank once or twice per day for frogs will provide enough humidity. Make sure the hygrometer your using is accurate, many I have found not to be. If you're using a heat source like a bulb or ceramic, keeping the tank in a warm room and lower the wattage is best.