Depends on how nice of a tank you want really, but Ill just list some stuff that you NEED.
-A ten gallon tank would be fine for one adult, but a 20 gallon long would be less cramped and give him plenty of room, if you can, Id go with the 20 gallon long.
-What I use for substrate is repti carpet, which is safe from impaction, and works fairly well. Another good substrate is slate tiles, which are much easier to clean that carpet, and look very nice. These also are much closer to what you'd find in there natural habitat than sand, which can cause impactions, Id stay away from this just to be safe.
-Your gunna need atleast two hides, one on the cool end and one on the warmer end. The cool end one can be anything they can ide in, the the one on the warm end must be a humid hide. You can make a humid hide by cutting a hole in a container and filling it with peat moss or potting soil. This helps them shed.
-A bowl of calcium(D3 free) They lick up the calcium when they need it. You also have to dust food items with calcium. a Good one that many people use is mineral.
-A water bowl
-A UTH. This provides the best warmth for leos as they enjoy the belly heat and helps them digest their food.
-A thermostat. With this u can control the temps on one side of the cage and keep it at a constand 90 degrees F.
-A screen top. Dispite being ground animals, leos can climb very well and escape without a screen top, this is a must.
-You can also Add branches and rocks that you buy at a pet shop, this will keep your leo busy, but isnt really a must.
-You can feed one of the following as a staple diet:
Superworms
Mealworms
Crickets
Crickets i find are a hassle and mealworms are alot easier to keep, and dont smell at all. You can provide a bowl of these for the leo to eat whenever he pleases, or you can have a feeding time every day. Superworms look kinda like mealworms, except alot bigger. You feed these the same way as mealworms.
You can also feed waxworms, though these are VERY fattening and shouldnt be used often. They also get addicted to them, and wont eat anything else. Pinky mice are the same, i only feed maybe one twice a month. Some leos wont take them.
Good luck with your leo, I think I covered pretty much everything. I also recomend you do a search one leopard gecko care, this will give you many different caresheets and tell you everything you need to know. Later
MaC