AutoCAD is good for creating 2D images of furniture into blocks, create plans (somewhat tedious), and develop drawings on a coordinate system (absolute, relative or polar coordinates).
On the other hand, 3D software like SketchUp and Revit are great tools, but it depends on what you want to do. SketchUp gives the user the ability to create models from geometric shapes, and it also has an enormous online library, from which you can download samples from other 3D Modelers. This way, you can download their furniture, and practice making your own. Lynda.com provides training for designers who need experience with CAD software, and I definitely recommend it.
Revit is a completely different story. Unlike AutoCAD, Revit uses a system that is known as BIM (Building Information Modeling). Basically, you write all the essential information about the floorplan on Revit's Properties Manager, and Revit will do the calculations for you. You do have the ability to create a floorplan, adjust the walls with your mouse, etc., but not in a coordinate system like AutoCAD, which could be sort of confusing. After everything is inside of Revit, as information, then Revit could create an architectural 3D model, based on the information provided by you, the designer. Revit calculates everything, from the type of wall, type of window, stair heights, truss and/or sloped roofs, and such. Another software similar to Revit is ArchiCAD, but I do not want you wandering to the unknown before having knowledge on AutoCAD and Revit first.
In addition to your need to create a floorplan, your other inquiry is about Room Designing. I do not know much about the Coreldraw programs, so I cannot say for sure on those.
Still, there is a new android app called RoomSketcher, which is a great tool for creating a 3D plan and organizing furniture within it. It allows any person to design a custom made room, on a 2D to 3D environment. As the person in charge of the virtual design, you first design the floorplan in a 2D view, and then switch from 2D view to 3D view, carefully placing all the wallpaper, flooring, furniture and accessories provided in the apps libraries. Think like, The Sims, for instance, where you buy the house, or build it, then you put the furniture, get some income, etc.,etc.,etc., but without the characters, of course. After the design is complete, you can save it in a library, and choose to set an image as a rendered image, or as a 2D plan.
RoomSketcher recently added a 360 degree feature, that allows users to save their work, and view it interactively through a 3D lens. That way, you can have a project to take notes and references on, while still keeping a floorplan, without having to erase all the furniture and accessories from it. This is essential if in the future, you want to show potential customers, clients, or vendors what your skills are and how you can get the best out of any room style.
If you want to use sophisticated software for interior design, try Chief Architect, which is widely used by many remodeling professionals. The only disadvantage is that Chief Architect has to be rented for $199 or paid in full. You could try a trial version, but think of the watermark features, and the time you have available to complete the whole project. My advice is to start playing a bit with the RoomSketcher app, and then use Chief Architect for more complex projects.