I want a probe or something to walk up to an obelisk and have it bring up a menu to change it into a variety of buildings. Right now I'm trying to get just the abilities and command cards set up so I can test it out. As of right now it's not going so well since I'm not too good with the editor.

Also so I don't create multiple topics, how would I make a stargate shoot out interceptors and keep them out and flying about the building until an enemy passed by?

You are asking for a lot of complicated things.

I would suggest starting out a little simpler and learning your way up. You can start with looking into the morph abilities (there are examples with the command center) for learning how to morph buildings into other buildings.

Look at how the Zerg buildings evolve, such as from Hatchery to Lair. This relationship is likely what you want for your cause.

As for the interceptors (and the above problem, too), you can use triggers to detect when a unit is in certain range of another unit. For your first problem, you would say a unit comes within range of a probe as the event, the unit type is an obelisk for the condition, and use "triggering unit" to reference the obelisk in the actions.

For the interceptors, you'd have to detect when an enemy is in range of a stargate for the event, detect that the unit is an enemy of the player owning the stargate, and then reference then order/remove the interceptors "into" the stargate. To check that no enemies are around, you'd have to have a periodic event with a condition that no enemy unit is in range of the stargate.

I found out how to do it. I used the information here and the information from sc2mapster and figured it out. But it doesn't change to the new building. It stays as the Obelisk. Would that have to deal with actors?

It depends on how you did it. If you used an evolve ability, then it should evolve into a new building with a different actor.