BTW you need to save a large chunk of IP for level 3 runes rather than just buy champions. Eventually you need a couple pages with optimal runes for 2 champ types, but with the default 2 pages its worth getting some that cover a decent amount of champions, like magic resist/level blue, flat armour yellow (and/or mana regen/5/level), armour penetration red, magic pen red and 3 flat HP quints.
To me the above is good to start with as its cheap and will be OK for multiple champions. If you know you will only play a particular champion it could be worth just getting whats good for him and build from there but then you might be stuck with runes that don't work that well for other champs.
You might want to get as well cooldown reduction blue, 3 armour pen quints, 3 ability power quints, ability power / level blue, health / level yellow, dodge yellow etc. If you only have 2 pages you might need to buy some more, or get the rune page bundle for RP