Item - Requirements

Hello
I making a map, which you can be 3 kind of heroes, Combat - Ranged - Magic.
But i got a big problem :(
The problem is that combat heroes can buy ranged items and magic items and magic heroes can buy combat and ranged and magic and so on. I dont want that.
I want the Combat heroes do only be able to buy combat items;
Ranged heroes can only buy ranged items and so on.

How do i do this? it dont seems to work with requirement upgrade or a unit needed. How?

Guess you can make a trigger:

Event:
Unit - Acquires an item

Conditions:
((Hero manipulating item) is in (Units of type [your unit])) Equal to True
((Hero manipulating item) has an item of type [your item]) Equal to True

Event:
[your event]

[your unit] = the unit you dont wish to be able to have [your item]