Snow globe help

[leftof-thedial.livejournal.com]

I'd really like to make a snow globe but I would like it to be square shaped and clear almost all around. What do you think I could use to make this happen? I was thinking of going to the local home depot and asking them to make me a box out of plexi glass, then I would glue the top on. How can I make sure it would seal properly? I've never done anything like this before and I'm at a complete loss. Help me, craftgrrls!