Let see...
1st - Fire Rocket -> Hero fire powerful projectile at target location, projectile will explode, dealing damage
[Main Attribute x this ability level] to all targets
[enemy, friendly, neutral, buildings] in small aoe
[100-200], ground will burn for some time dealing minor damage each sec t same targets!
If targeted unit isn't building it can be knock backed due effects of explosion and stunned for very small about of time
[0.01-0.5]!
2nd - Remote Mine -> Hero can place mine on ground that will explode only when triggered doing same things like spell above - (max placed mines can be set to 5 or 7)
3th - Dwarf Skills -> Improve other spells: Add damage, increase attack range, max number of placed mines, reduce cooldown, add agility to hero etc etc!
4th - Build Defense Tower -> Hero need few sec to build some kind of tower (building), he will be placed on top after finish! Hero will be unable to move but his range and sight radius will be increased! He well be also able to detect invisible units (if he can attack at 2000 range he can detect on 1000 or something like that)! Tower has small hp
[300-500] and armor
[0-10]! Only one tower can be used in same time, last created must be destroyed (player can click destroy or something like that if he want)! Only hero can use this tower others heroes can't! It cost loot of hero mana (maybe even some gold if you want to create some crazy heroes in future this one will be good for start

)
Well this one is my idea, if you don't understand everything just ask