I want to buy him, but when I see some Blitz all are complety differents.
For example I saw pure support, pure mana, pure tank and few AD Blitz.
Which is him best role?
And plz help me with the build.

Support Blitz is the way to go, especially if you have a bursty AD carry (Graves, Corki, Ezreal, etc.)

Mana Blitz just makes you tanky, nothing else. Support Blitz's initiation is just as good as tank Blitz; the only time I'd ever recommend tank Blitz is if the jungler and solo top are both super squishy. AD solotop Blitz is a good troll build, nothing more.

Support Blitz should build Faerie Charm or Boots with wards as a start into Philo/HoG, Shurelya's, Aegis, and then you can choose from stuff like Zeke's, Frozen Heart, etc.