I applaud you in doing your homework prior to acquiring your pet herp! Too many times owners impulsively acquire a reptile, and then go scrambling to find the appropriate habitat, heating, lighting and correct food items.
The young leopard gecko (Eublepharis macularius) should not be kept on sand for at least the first six months of life to prevent impaction problems with substrates. A glass aquarium works well for a leopard gecko, and a 10-gallon tank is an appropriate size for a single adult gecko. Many people breed them in plastic shoeboxes or storage containers, but for viewing, a tank or plastic cage is your best choice.
For heating your enclosure, you have several safe choices. While some herpers recommend never using “hot rocks” for heating, the newer ones have built-in safeguards to prevent overheating and hot spots. The electronic heat stone (by Exo Terra) has an electronically controlled heating element that automatically shuts off when a certain surface temperature is reached, which will prevent burns and overheating. The heating element is fully encased in the stone, which prevents hot spots, and the resin it is made of ensures even heat distribution.
However, I don’t think that one hot rock is going to provide enough heat to create the temperature gradient from 90 to 75 degrees Fahrenheit that is appropriate for leopard geckos. At night, the temperature can go as low as 64. To provide the correct temperature gradient, you can utilize an under the cage heat strip designed for desert terrariums. These substrate heaters are also designed to be very safe and also provide even heat distribution. Some herpers also utilize a 40- or 60-watt incandescent light bulb in a reflector fixture as a means of providing a focal heat source for the habitat. A red bulb can be used to provide some heat and also allows you to observe your nocturnal lizard (meaning that they are active at night) without disturbing their normal sleep-awake cycle.
You can use a heat strip, heating stone or incandescent bulb, or any combination thereof, to create the correct temperature gradient for your particular habitat. Make sure that you have several accurate thermometers/hygrometers in strategic locations around the habitat so that you can monitor the temperature in the different zones.
geckos are from arid regions of Pakistan, Afghanistan and India, and therefore do not require much humidity (except in their hidebox, which can provide a small area of higher humidity, which is very helpful when it comes time for shedding). You can provide a small margarine-type tub with moss, vermiculite, sponge, perlite or soil in it, with a hole cut out for an entrance, or you can purchase a hiding cave. Mist the hiding area frequently to boost the humidity.
Keep a shallow dish of water in the habitat at all times and make sure that it is not so deep that your lizard could drown in it. Many keepers also keep a small dish of a calcium supplement in the form of a fine powder, which leopard geckos will often readily consume from time to time.
Because leopard geckos are nocturnal, most people don’t provide them with full-spectrum lighting, and instead, offer them a vitamin/mineral supplement that contains vitamin D3 (which they would produce when exposed to the proper ultraviolet spectrum of UVB light). But, you can provide them with a full-spectrum light, which also emits some heat and should be taken into account when planning your setup.
While I don’t raise leopard geckos anymore, I do keep viper geckos, and they too are nocturnal. For their setup, I use an undertank heat strip, plus a compact full-spectrum fluorescent light, which I keep on during the day. This combination provides them with the correct daytime temperature as well as the night-time gradient. They do sleep during the day, usually in overturned flower-pots, but I think that they should get some benefit from the full-spectrum lighting.
When looking for your new pet, make sure that you pick out a healthy specimen. The tail should be fat (approximately three-fourths the thickness of the neck), the eyes should be bright, and it should have all its toes (make sure that the toes don’t appear abnormal or stuck together, or have old, dead shed skin adhered to them). Look for one that is alert (even though it was probably just awakened). I wish you a wonderful, long relationship with your new pet gecko. They are great pets and are quite long-lived (they can live to be over 20 years of age with good care).