She suggested that the best solution would be a deck, which I am not tempted by, both because of cost (it would not be a DIY project) and because it just doesn't seem to look right for the back corner of my yard. Her second choice was to level with gravel and top with crushed rock or pea gravel, trying to minimize use of the compactor, at least in areas with known roots. (I'm not sure why she didn't mention wood chips or mulch -- perhaps for same reasons one doesn't want to put topsoil over tree roots?) I take it that with any of these, I could pepper the area with stepping stones without causing problems. (Grass is apparently not an option, as it would require laying a deal of topsoil over rooted areas.)

Having done hours of reading in these forums, I've found that all of the available options have a lot of detractors out there. Pea gravel, if loose, is a lousy walking surface and a pain to get debris out of. Crushed stone and decomposed granite track into the house. (Though it's a 60 foot walk to the door in this case.) My childhood experience with a shady area covered with woodchips was that it tended to be damp and messy and full of bugs, though with the gravel going down in this area, it should drain well, and I've recently seen some very nice mulch paths at local nurseries. And I've come across people saying, for each of these products, that they've put them down, hated them, and then found it an awful chore to remove them and put in something else.

So I'm asking for advice to try to satisfy a number of worries.

- Most important is not damaging the elms. I'd rather have the elms than the patio, but don't want the area to just be an unsightly mudpit when the debris from an old shed is removed and the woodchucks evicted. (I know, lots of luck on that one!) I take it this means minimizing excavation and compacting, and no topsoil around the roots.

- Being under trees, there are going to be plenty of leaves in the fall. (The deer and woodchucks seem to be very helpful in tidying up those that fall in summer.) I need a surface that can be cleared with a blower without taking all the surface with it. (Luckily, the back edges is forest, and I don't have to blow rocks or chips into the grass, but still, pavers would have been so much easier.)

- I envision it mostly as a sitting area with a bench or two, and perhaps some pacing. So it needs to be able to be kept level enough for some furniture, and preferably drain well enough that one can walk there without getting shoes soaked.

- Since there are lots of groundhogs in the vicinity, closing up the hole in this space may not be a lasting solution, even if I'm lucky enough that the construction process scares off the current residents. (One reason I initially liked the idea of 24" concrete pavers. Wondering if putting down 3" wire mesh under the surface would do the trick....)

- I hate things that can't be undone. The area needs some leveling willy-nilly, and I'm thinking some gravel is needed in any case for that. I've gotten the impression that some crushed stone on top of that might be most flexible, in that it could (I think) be topped with a thin layer of pea gravel or a layer of wood chips later if I don't like how it turns out. (Am I right that pea gravel would need to be removed to put in a different surface? And that it would not be wise to put gravel or stone on top of mulch at a later date?)

- I have seen permeable pavers -- the ones with the diamond-shaped holes in them that get filled in with grass, dust, or stone -- but don't find them appealing. I'm not sure how much loss of permeability there would be if I spaced pavers with gaps of an inch or two between them, filled in with gravel, or whether this would be a good surface in any case.

I fear there may be no optimal solution for this area, and that I have a choice between endangering the trees or using high-maintenance surface materials. But I'd be glad to hear that I am wrong, or for that matter, that one option is considerably less bad than the others... Any help is appreciated.

Have you tried the trees forum? I think knowing what could or won't harm your elm is the first thing which must be answered. The last thing the world you want to do is injure or compromise a mature tree.
I recall seeing in a landscaping book a wooden bench built around the trunk of a tree--and I forget if there were slices of stump used as paver or what...but you might want to take s look at the landscaping section of your library.

I think the deck idea was probably the smartest idea, given your aversion to pea gravel and granite. I've built decks (5'2", female, almost 50). All you need is a good sliding miter saw, a level, and a good driver (power drill screw driver) and its a easy job.

If the health of the trees is the most important thing, a floating deck would be your best bet. Depending on the shape and size, it shouldn't be that difficult to build if you can use a saw, level, and drill.

Can you level an area without excavating? Maybe a frame made of PT 2x ? or granite blocks, like a raised bed, that is then filled with gravel?

Crushed stone that varies in size will stay in place best. Pea stone rolls around and doesn't pack together.