Trading Trigger

In a map im making, i want to know how to make a trigger (and with at least 2 spells) to basically give the effect of trading. (kind of like in Age of Empires with those merchants ships and the carts.) I want one ability that will target trading post (building) as its home building (returns its goods to that building) and the other the target building (where it goes to to get the goods), and when it returns i want it to give gold to the player, and after that it will patrol to and from the two buildings.
(here are the abilities/variables I have)
Abilities:
1) Select Return destination
2) Select Target destination

Variables:
1) HomeBuilding
2) TargetBuilding
3) TradeAmount

Also, on the variables would i have to put arrays?

can someone respond to this please.








(P.S. Srry for double posting)

If I remember how Empires does it, you'll need to run a check when the building gets built.
Building A is built.
If there is a Building B of same type owned by another player then:
Create trader, order trader to patrol between Building A and Building B, set custom value of trader to 1.

Trader comes within 200 yards of Building B and custom value is 1, set custom value to 2.
Trader comes within 200 yards of Building A and custom value is 2, set custom value to 1 and add 100 gold.

I hope you get the idea. It can be done with items if you want to add the extra touch.

I think what you want to do is make 2 custom abilities, one called Trade (Get Goods) and Trade (Deliver Goods)

Then he starts with only the (Get Goods) ability. Then he has to use that on an enemy market. When he uses it then the (Get Goods) ability is removed and the (Deliver Goods) ability is given, which he can only use that on his own market, and is ordered with the trigger to use it on the closest friendly market. Then when he uses it, the player gets gold, and the (Deliver Goods) ability is removed and the (Get Goods Ability is given), and he is ordered to use it on the closest enemy market.