There are grates made of heavy-duty recycled plastics these days. They're no maintenance too. (Metal ones would probably require some in due time ...)
Anyways, the keys to the successful installation and 'operation' of a window well is for it to be dry AND drainable. If it's always wet or wet for prolonged periods of time, you'll have new problems. So, assuming you've covered that base, you can then cover the well. I would suggest that you stay away from those flimsy, plastic covers that you can buy at Home Depot, Lowes, and the like. Visit a Lumber Yard for the more heavy-duty plexiglass covers.
Visit here for some high-end guidance. Window Well Covers will keep you busy! My best to ya and hope this helps.
Jay J -Moderator
PS: Hopefully, you have the proper sloping of your landscape all around your window well ...