i agree with moe88, although both these geckos don't like humidiy,leopard geckos live in savanas in India, the fat tail lives in the sahara desrt in Africa. but you may ant to keep the lower levles of the substright a tille moist, they do like some moisture, play sand it the best substright for both and cati and suculents will grow well in them, make shure you lay down a 1-2 inch layer of gravle 1st, this this is for draned, then put down plastic window skreen matereal to seporate it from the sand, now you but down any heay objests like rocks or fake rock caves.then put down like 4-5 inches of sand. now you can plant you cacti and suculents and they may be down an accent like a peice of old drift wood (Cholla Cactus Wood looks realy cool), some dryed grasses and a water bowl. this woukd be fine for eather leos or fat tails, you could keep about 4 of eather, just make shure you only have one male in the tank. position a 100w basking light on one side, this side should be about 100-110 degrees, you can have like a 75w cacti grow strip light for the plants, as long as it does not go below 75 degrees at night you should not need any outher heating
good luck and have fun!!!!