RUNE TROUBLESHOOT! D:

Tom here. I've just reached level 20 and am now ready to buy runes. I play Heimerdinger and so I was looking in the ability section, and others of course too, and I see a lot of +4 of a certain thing runes. (EX: A rune would be +4 ap) And I was thinking...would that even be worth it? +4 of anything wouldn't seem like that much...so I am confused about what runes to pick! D: If you all have any examples of a good rune, or any rune ideas for Heimerdinger, I would REAAAAAAAAAAAALLY appreciate it guys. Thanks! I ruv u forever