You have the shape already.
Window select round it to select it all, then g (shortcut), or R-click/Make Component.
Go to one of your existing black panels. Open it for editing, start the paint Bucket tool (shortcut b), press and hold the Command key (on Mac), to sample the black.
Close that component. Re-select the irregular component you’ve just made. Open it for editing (double click it, or R-click, Edit component).
Press b again to reactivate the paint Bucket too. Apply it to the top face and edges. Or preselect them by triple click when the component is open for editing, then apply the paint Bucket.
Do the same for the small irregular part next to the larger irregular panel.
I notice that your ply panels have skewed axes (shown here for clarity in Monochrome)
You should open any one of these component, Change Axes, and reset the axes at one corner, along the edges of the panel.
Also, see the post I recently made for another beginner in SU.
Help getting started.
You may find it helpful in dealing with components, naming, and the use of tags.
I notice Z-fighting on all your rectangular black panels. (They shimmer as you orbit around). Looks as though there are two faces in the same place ‘fighting’ about which one should be shown as higher in the Z-direction.
Yes, there are. You haven’t deleted the original face of the floor. This is what I see when I turn off the tag for the panels -
8 X 4 PLY SHEET STAINED BLACK
Delete the parts of the floor you have replaced with unitary panels (that’s pretty well everything else).
But part of the floor is the piece I just made into a component, showing black.
I see in Outliner that you have given the same Instance name to all the floor panels, whatever their size. They aren’t all now 8x4 panels -some are smaller or irregular.
I don’t normally bother with instance names at all - you could delete them all without loss. Or, if you want to be clearer which are small rectangular ones, you could give those a different Instance name, depending on their size and orientation.