How do I start working on italics?

I'd like to start working on italics for my font (Portfolio Mono, see a separate thread).
The problem is I've never done italics before, so I'm not sure how to approach this task.

It's going to be true italics, but related to the roman enough to consider the roman as a starting point.

I'm considering starting from:
1. scratch.
2. the roman slanted.
3. the roman manipulated by some fancy tool that is supposed to give better results than simple slanting.
(Am I missing any option?)

How would you approach this?
Any tips?
What tools do you use for better slanting?