What would you recommend for a Bloodelf Rogue Levelling Build?

Well I'm still kind of a noob when it comes to rogues myself, but if you like killing stuff fast, but with less reliability, go daggers for backstab.

If you like killing stuff a little slower, but with more ability to handle adds (monsters that attack when you didn't plan on it) go combat swords.

For levelling I recommend combat swords. Start with improved sinister strike. Then take improved gouge.
Then precision. Then you should have a feel for what you like.