I am not sure of your geographical location but I am from upstate New York and have had success in both indoor and outdoor ficus trees. When I first had started buying house plants my success rate was probably at an all time low. Many variables to consider though (like an ex that would ALWAYS leave the AC on). But we won’t go there.
I have found that the ficus trees do indeed flourish and grow faster if kept outdoors primarily in full to partial shade. These are my larger and heartier trees of all by far.
Indoor lighting was a must for the ones inside. I have used fluorescent tubes as well as HPS's (high pressure sodium) for this BUT, the most important key factor in this all is humidity. Every day, sometimes several times a day in passing I mist the leaves. They love the humidity ! I tend not to water the soil too much. Allow your soil to dry out then saturate it when water is needed. Allow the soil to dry again and repeat. Too much water in the soil will promote root rot and/or bacteria buildup in the soil which well definitely kill off your plants.
Keep with it and experiment with different locations as well as watering cycles to see what works well for you. It can be relatively expensive to keep buying new plants not to mention the harboring of nasty pests and bugs, so my suggestion to you is take clones. Clone the plant by either taking a clipping and allow part of the stem to soak in a cup of water until it roots or purchase "rooting gel" at your local greenhouse. Place some of the rooting gel on the freshly clipped stem and place in either a cup of water or in soil. Some green houses are starting to carry "pods" now. It is an organically made compound that is formed together to hold clones or stems in the pot. You can eventually replant the stem with pod attached into regular soil once it has rooted. They work great! Oh yeah, if you are choosing to clone then keep the clones under a fluorescent light 24hrs a day for the first week or two. This promotes the vegetation cycle of the plant and assists it in growing. Keep us posted in your growing endeavors.