How finished does it need to be? Could you simply cut a piece of plywood to the exact size, paint it to match the wall, and hinge it at the top? It would lift up out of your way and you could use hinges that hold themselves open like for toy chests. Or you could add a brace to it and then when it's open you would have a counter top surface too.

Great Idea! Thank you. Let me think about it. I would be able to put something together but also looking for something professionally build. Maybe something like this:

I have this for my breaker box and it looks nice. However it was my house when I bought and I don't know where to get something like this

That said those covers maybe too fragile for this purpose

You can order a prehung door the size you need for as long as it's a flush door and all you have to do is trim it out.

You or any carpenter can also make a door the size you need from a flush prehung door or make your own frame and cut the door down, etc.

You can also cut a prehung metal door, if custom size ordered they can be expensive, but if you get an exterior prehung steel door they can be easily modified to fit any height opening.

You need a door for under your ladder in the basement? What does that mean?