Creating a simple furnished 3D building with Sweethome 3D is quick. More complicated buildings take more time. Knowing how to use levels, then walls, then adding rooms (creates ceilings),then adding "furniture" and then putting on a roof are necessary steps. Furniture includes windows, doors, electrical stuff, stairs and such. TJ Free provides a useful series of YouTube tutorials https://www.youtube.com/watch?v=ngSHLJ5 ... 39MrANKxx_

Youtube has other useful how-to videos, and examples of people's building models. People on this forum are very helpful with specific problems. The forum archive is a treasure of information and has a good search function.