I want my 3 ft single stem Fiddle leaf to grow into this. How do I start? Currently the single stem has the traditional alternating leaves going up the stem from the bottom to the top.
Pick a leader that is perfectly vertical, or can be made to be perfectly vertical at the next repot by changing the planting angle. Then, make sure it grows straight. As it develops, you'll need to pinch all branches other than the leader - that, you'll let grow until it's about 3/4 of the ht @ which you wish to maintain the plant - then pinch that, too. As the tree grows, you'll be removing the lowest branch occasionally. Remember that these lower branches are going to be giving the trunk thickness and strength, things that are important under low light conditions, so don't be too quick to remove these lower branches. Once the tree is 3/4 of it's intended ht, let all branches grow to at least 4 leaves, then pinch them back to 2 leaves. This will make your tree as full as it can possibly be, within the limits of the light and other cultural conditions you supply.
Everything is pivotal on your being able to keep the plant healthy, which is going to require some effort to learn a few things on your part ..... like how to maintain roots to keep the tree healthy. Maintaining vibrant and healthy plant material over the long term is no accident.
I'll link you to a thread about Ficus in containers. If you find that interesting, there are two other threads you will undoubtedly find helpful, and I'd be happy to link you to those as well.
Here is a link that might be useful: About Ficus in Containers .....