First, a couple of remarks:

• How much memory a modules uses is generally dependend on what you do with it, after you load it.
• Deleting packages is unreliable AFAIK.
• Freeing variables, namespaces etc. in Perl does NOT in general decrease the amount of memory taken by the perl process.

I do not know of a standard way of accessing this data, but when I have a need for it, I usually run top (or equivalent resource monitor for other systems), and execute the code to see how much it takes up. You can make it a little easier by sending out some messages about what the program is doing (i.e. which modules are being loaded) and then sleep()ing for a couple of seconds. I haven't found a real need for anything more sophisticated.

YMMV
Joost.