Stuck trying to find folder sizes

I am currently trying to learn powershell and as a side project I decided I want to create a script that checked the sizes of each subfolder in a folder and deletes any over a certain size. I am currently stuck trying to get each subfolders size and was wondering if someone could help point me in the right direction or tell me if I am totally off. I want to use this as a learning experience so I am not looking for an exact answer. I currently tried two ways: This way I get the size of the all the folders combined: http://pastebin.com/bFmrS8KK

This way I get no output at all: http://pastebin.com/ruXdcQdb

Please let me know if I am way off base and need to rethink the process.

Edit: Using Window 7 powershell version 3.0