I'm trying to start my model with a basic flat plane to represent a floor. It isn't a square room, there are alcoves and other things that make the room irregular. I've been trying to work out how to create such a shape in Blender and nothing I'm searching online comes even close to showing me how to perform what really ought to be a pretty basic task. Here is a sketch of what I'm trying to draw.
The measurements are there because I need it to be fairly accurate as it's based on a real room where I need to place furniture etc.
I've started by creating a 2743x3625 plane in Blender, and I want to remove the two cutouts, one in the top-left, and the other skinny one on the left side wall. I thought I could do this by creating two more planes of the appropriate sizes, positioning them and using the Boolean tool to subtract them from the main shape. This doesn't seem to work however, even if I extrude them to 3D shapes and try that way.
I've also tried adding loop cuts, but I can't manipulate those accurately enough. If I try to set a position, it does so relative to the middle of the plane where it starts. Am I stuck with this method?
Is there some other/better way of doing this? Ideally this shape would be a single plane, not a bunch of planes grafted together, but I don't know if this is possible like it is in other modellers. Any help will be greatly appreciated... I'm pulling my hair out.