Both builds are definitly not viable for rankeds! Play them at own risk.
I'm not 100% sure if a i calculated the Health of Alistar corrently. I added all the flat bonus values (6007,76) and multiplied this with all percentages together (28%) and added the Base Health (2278):
(6007,76 * 128 / 100) + 2278.
If there is a misstake, feel free to edit this answer but provide the calculation formula.
Alistar (without any skills involved)
the most health any champion can obtain is 9967,9328, being a level 18 Alistar with:
Base:
Runepage:
Masteries:
- Veteran's Scars: 36
- Juggernaut: 3%
Items:
- 5*Warmog's Armor: 5000
- 1*Spirit of the Ancient Golem: 200 and + 25% Bonus Health
- Elixir of Fortitude: 235
unlimited health with Soul Furnace
the most health any champion can obtain is 13195.95, being a level 18 Nunu with:
All health runes and masteries:
9 Scaling Marks of Health (+87,48HP)
9 Scaling Glyphs of Health (+87,48HP)
9 Percent Seals of Health (+216HP)
3 Percent Quintessences of Health (+145,8HP)
3 points in Veteran's Scars mastery (+36HP)
1 point in Juggernaut mastery (+3%)
5 Warmog's Armor (+5000HP)
1 Spirit of the Ancient Golem (+200HP +25%)
An Elixir of Fortitude (+235HP)
Wild Growth cast by a Lulu with the maximum amount of ability power. (+???HP)
Consume cast on a Golem jungle creep (+10%)