I've done some math for a level one melee character based on using runes of all attack speed, all damage per level (but for this example flat rate damage) and all crit chance.

the rest is left up to you but numbers never lie.

(this is based off of my level 23 summoner)

Criticle Chance

all 7 red = 6.51%

all 7 blue = 1.96%

all 7 yellow = 2.94%

and two quintessences

totaling 15.13% at level one.

while this is impressive it leaves alot of chance and relies on the partnership of attack speed.

Attack Speed

all 7 blue = 4.48%

all 7 yellow = 6.3%

all 7 red = 11.9%

and two quintessences

totaling 27.86%

this equals out to about .799 attacks per second. While this is fairly decent, it leaves something to be desired with damage.

Attack Damage

(you get the gist of my numbers so I'll sum it up)

Totaling 9.718 (if this game rounds) 9.72

in this example I'm using level 1 stats, I'll look up more mechanics and such for level 18 and level 8 stats. (level 8 because it can be a turning point or 10 if you prefer.)

also note that in this example I'm using an 8 second timer for attacking. (Since it doesn't take too long to kill a foe)

For Attack Speed in 8 seconds you attack a total of 6.392 times, and since attacks don't round in the end result, its 6 times. at level one the base rate for damage is 56 so totaling to 336 damage. With no criticle hit chance.

For Criticle hit chance in 8 seconds you attack a total of 5 times, for 56 damage totaling to 280 with a 15.13% criticle chance, allowing atleast one criticle hit to land. dealing 112 damage instead of 56 so totaling up to 336.

For Damage 5 attacks of 64 damage totaling 320 damage. With no criticle hit chance.

for later levels I'll need a more comprehensive grasp on the game mechanics.

for this example I used Master Yi's base stats for level one.