It has a plexiglas sheet (1/8th inch) with about 20 little holes for ventilation in it. I use only one 45 watt outdoor flood bulb to heat it period. The basking spot hits 200f on a warm or hot day and 195 or a bit under on a cold day. The cage has around 8-10 inches or more of dirt in it (kinda hard to get alot more in there and keep a decent temp gradient or give the animal room). The basking light is mounted inside the cage to keep heat inside as well moisture as an open screen top is a recipe for lizard jerky. Heres a test to perform at home, take the animal out for a day, in that day place a piece of raw meat in the cage with the screen top, check that piece of meat the next morning, it will be dry and hard (jerky). The idea is to demonstrate what is happening to your lizard and may be a big part of its growth problem as well a long term serious heath issue (Ive buried a few in the past before I learned about the effects of dehydration on monitors long term). When you use a high wattage light and or heater it causes the air temp to go high throughout the cage causing the cage to have no temp gradient (room temp one end, 86-90 on the other end), it also causes all of the heat and humidity to rise to the top and out with no closed top. Theres way to much heating involved in that cage, youll notice a difference in electric bill also by lowering wattages of bulbs and they will last longer. Heres a 45 watt halogen outdoor flood like I use...

This is a 50 watt indoor flood bulb which cost about $1.99 and I use them in smaller cages..

I also use $1.19 ceramic light assemblies to make basking lights from a hardware store, just add a cord and mount...
This is the ackies cage for now, but you can see the plexiglas sheet, the basking temp, the air temp is about 90 around the lightbulb, then drops to 72 on the other end on a cooler day..

Monitors love to dig and burrow, so use field dirt mixed with about 10% sand, mixed with some from a creek (or river) bank and make it deep, your monitor will outgrow that cage fast.
Aspen mulch is a lousey substrate as it is dry it moesnt hold much if any moisture. I know people who use cyprus mulch but prefer dirt as soon as they tried it. Astroturf, thats not even a decent substrate, thats not even a substrate, anyways thats stuff is no good for them. Be prepared to start building a bigger cage when you get the animals set up close to properly, it will be active grow and dig. Good luck, keep in touch and let us know how it works.