Warped UV for simple model [Update: The original had lots of extra vertices for some unknown reason. I recreated the object from scratch to remove them. .blend file and images updated.]
I'm trying to create a UV map, and it always ends up warped.
Are multiple independent seams allowed? If so, I'm at wits' end.
I tried creating the object a number of different ways. This particular one was created from a cube, moved z face, extrude x face, extrude y face, limited disolve, inset z face, extrude inset z face.
Complete beginner!
Tile9d.blend


Expected:

(I can always condense that by splitting it into two and flipping and rotating one of them.)
When you are UV unwrapping, you're basically trying to flatten out a box. You can cut seams around all six faces, but that leaves separated parts. Try to find the edges where the geometry has to spread and mark those as seams, like this:

You can see I made seams down the 45 degree bevels, and just cut the bottom out separately.
After removing all the extra geometry it becomes much easier to achieve the UV layout you wanted: