You first buy "Dorans Blade" at the starting of the match. After some time has passed and you got enough money you go and buy "Berserker's Greaves", but if you don't have enough and you recalled back see if you have enough for "Boots of Speed". From "Boots of Speed" you upgrade them to "Berserker's Greaves" and you are ready to move for your first "Main Item" which is "Malady". Don't worry for money, you can build this items from 2 "Dagger" and 1 "Amplifying Tome". After the first item, you start rushing for "Wit's End" which can also be bought by "Recovery Bow" and "Null-Magic Mantle". After getting the "Wit's End" you collect money for "Madred's Razors" which costs 1000. After getting that you you might want to get "Recovery Bow" again, this time for building "Madred's Bloodrazor" because it is quite expensive item.
After getting all those items so far.. You might wanna check the status of your team and their team and build situational items. For late game I suggest to sell that "Dorans Blade" which was the starting item and get item like "Hextech Gunblade" which provides more attack dmg and Life steal with some ability power also.

Why to take Ghost?
- You can get away fast and/or catch people and gank fast.
Why to take Ignite?
- Simple reason, Always your Toxic shot is not enough to take them down and Ignite is always good damage dealer

Alternative Summoner spells:
Smite
- For jungle Teemo
Heal
- For newbs
Flash
- To gank or get away
Exhaust
- To provide good slow on enemy
Teleport
- To teleport fast on different lane