While there are software packages out there, they obviously cost money and I am not decorating a mansion, so all I could use is a simple utility.
Raymour and Flanigan, which is a furniture store that I’d never heard of before today, has just the tool. Their Room Planner allows you to basically create virtual rooms by inputing your dimensions. Once that 2 second task is done, you can begin adding furniture, doors, plants, etc.
It’s free to use and you don’t even need to register. Here is a representation of my home office: