The idea is to make keepers able to specialize in 3 different paths. The keeper can only choose one path, for that reason many rooms and creatures are path neutral and accesible by all keepers (hatchery, treasure room...), same for spells like create imp, healing or ligthning . Each path will have special bonus, rooms, spells and creatures, the player can decide wich one to take at the start of the level and researching on a library is the only way to advance on it. When the total number of research point passes a quantity, the ability that needed a certain amount of them gets unlocked (ex. 50rp fireball, 100rp thunder., 200rp war-room...).
Possible development of paths:
Path of war:Brawns over brains, emphasis on melee troops
Bonus:
Cheaper creature wages
Cheaper lair and hatchery construction
Extended max number of creatures (high on the research tree)
Rooms:
Arena -> attracts ogres; make orcs become warlords once they pass certain level
Barracks-> attract minotaurs
Fire pits-> Imps become firelords (a mixed warrior-mage)
Spells: support only
Mass healing
Rage
Protection
Crusade
Path of magic: we have a good couple of fireballs, more magic users and undeads
Bonus:
Cheaper libraries
Undead have low wages
More mana generation
Necromancers and liches can rise zombies and skeletons from a dead creature on the spot (only living and humanoid creatures)
Rooms:
Hall of bones -> Attract bone golems, Skeletons promotes to Death Knight, ; once they pass certain level
Hall of flesh-> attract abominations, cultist becomes necromancers
Dark temple-> warlocks becomes liches
Spells: mostly damage dealer and a few curses
Path of Stealth: a balanced mix with invisibility capable units
Cheaper casinos
Gains a small amount of gold constantly
Expert torturers, faster conversion
More traps and defenses than the other paths
Rooms:
Den of thieves: Attracts Cuttroaths, promotes goblins to goblin rogues
Safe-room: Attracts Shadow Knigths, promotes Imp to "Shadow Lord"
Room of horrors: Attracts our OD "Dark Mistress" clone? because we need a sadistic lady

Spells: a mix of damage support and curses
All of the above is a possibility, its nothing that i can decide alone, so i would like your input, thanks!