Hello Mac....
Don't want to be negative here but i think you have asked the wrong question. To be honest, forum members will pass on this post because they don't know what you want. I know i am not sure what you really are asking for. Do you want to model the moon? Maybe the ocean or a mountain? Are you thinking of military or civilian? It's a very open question.
What your asking is just way to vague and a really hard question to give the right answer to, personally i think you need to be more specific There are just to many senarios. I am sure everyone here has a million ideas for dioramas. I know i have plenty of my own. What you are asking i don't think anyone can answer for you. If i am right, people on here will find it hard to know how to reply. It's not that we don't want to help, this place is a fountain of knowledge and advice. You need to start the ball rolling with an idea of your own, don't care if you think it sounds silly, just put it on the table, then modelers here will add to your thoughts and give you the pros, cons and how to's.
Don't depair, lets just consider a couple of things.........
The first inklings of an idea for a diorama can come from so many sources. A movie on tv, a picture in a book, a story you read somewhere, a photo of a vehicle can inspire and sometimes best of all...... your imagination... Look around you and you will see diorama ideas in every direction.
Have a poke around in some books or on the net and find something that catches your eye. Do you have a vehicle or something made up that you want to place in a dio? Give us all a time/era ( WW2, Vietnam, etc ) vehicle type ( Tiger tank, Abrams, an aircraft) or maybe a particular type of terrain ( river, snow, desert, mountains, etc ) you think you could do, maybe it's just a bunch of figures, and we will attempt to steer you in the right direction. Also tell us the scale. That could make a huge difference to how you lay out a diorama.
Don't be discouraged. Start with something simple and let's see what we can come up with. I think though your the one who has to, as i said, start the ball rolling... You must have something in mind....
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Modeling is about what you want and like to do. It's great to look at others and learn but developing your own work is what it's all about.
And you have lots and lots of foam to use....
Imagination is the limit....
Hope all that makes sense...
Boomer...