I just finished converting my basement stairs into a bin. It's easy to fill as I just back my truck up to the exterior door, remove the top step (on hinges) and pour. It holds about 2500lbs. There is a hinged door on top of the bottom step that opens when I need to fill the stove (see picture #2). It took about 3 hours to build and I re-used most of the material from the old steps.
Is the access to remove coal through the lower step you show open in the last photo?? if so, make sure you have enough room to scoop the coal out with a bucket of your choice.. you don't want to have to use a small shovel to scoop out the coal..
Another way to access the coal under the bottom step would be to put a shovel-sized access door under the step at the floor level, this will allow you to get all the fines and last pieces of coal off the floor of the bin..
I think your idea is going to get quite a few people thinking about their basement stairways...
Greg, thanks for the comments. I realized that I got lucky after I read your post. I just checked and the opening and it's wide enough to fit a 5 gallon bucket in. My stove's hopper is only about 3 or 4 feet from the opening, so I may just use a large grain scoop. I do like your idea about making an opening for a shovel. That may me my first modification. thanks
Nice looking bin Davidl. I would suggest you devise some way to prop the lid open that won't pop out and smash your fingers or worse, your head. I think in terms of general appearance, you should get first prize.