Custom Buttom

How do I make a custom Button? Like inside buildings? Say a building has a button and when that button is pressed a message shows up

just make a building have a clickable ability
and do atrigger that recognises it when its been clicked, then text pops up

Make a custom ability that targets nothing, like stomp, then remove all damage, buffs, stun, etc. from that ability, then give it to the building.

Then

Trigger
Event
--A unit finishes casting an ability
Conditions
--Ability = Custom Ability
Events
--Display <text> for whoever.

yup yup yup

or u could do 3d text :D