Cause im with veigar i have tried Mana Flow + Presence of mind +
+ 2x 
And im still getting lack of mana every 3 minute just because im stacking with Q only that and 1 Q = stack 2 AP or 1 AP
Build a Lost Chapter instead. You're building mana regen (which means you will have to wait for your mana to regenerate). Lost Chapter (and Morello) both give flat mana.
His Q gives small stacks because with CDR, it's a reasonably spammable ability. Even then, it gives a small amount of stacks because he gains stacks through hitting champions with all four his abilities.
how is the cooldown / mana cost of a skill / damage of skills based on?
The cooldown, cost and damage are dependent on a champion's kit/"power budget". For example Taric's ultimate has a large mana cost and a large cooldown because of how powerful it is (AoE invulnerability). Or even Shen's Stand United. It eats up a large portion of his kit's power budget so it has a large cooldown and the rest of his kit is much less powerful to compensate for the power of his ultimate.
how did they work on that for 140 champions?
It's all part of champ development
the more crazy the cooldown?
General rule of thumb, the more powerful the spell, the higher the cooldown.
like yasou have no mana, ok what is the reason?
He was simply designed to be manaless. He has his flow meter. Champions like Vladimir and Zac have no mana because they use their health as a casting resource. Champions like Riven and Katarina are gated by their cooldowns.
yasou q 1 sec cd, ok what is the reason? no one knows, only dommys plays
His Q is basically an auto attack. It's supposed to have a low cooldown.
