towers that upgrade to something else

I was able to find a trigger that would allow you to setup where a tower after upgrading, could end up as something else. Here is the problem that I am running into. I need a base unit tower that can attack. The human scout tower has no attack, but it is currently the only tower that upgrades. I tried using the undead town hall, but when it upgrades, it looks funny and the towers end up doing some wierd stuff along with leaving creeps. So the question is, I need a way to make a basic tower that has an attack and can upgrade. Is there a way to add an attack ability to the scout tower or is there a way*that has been discovered recently* to make a tower gain an upgrade button? I noticed in one tower defense map that there is the ability to sell towers. Could this some how be converted to a upgrade option? Any advise would be appreciated.

Most people either design special buildings for each "upgrade" then, replace one building with another.

Others use the same building and change the abilities/attributes of the building for each "upgrade".

You can make your own upgrade button. which can trigger the upgrade.

well, yes, I was hoping to just use the guard tower and use it over and over, but I don't know how to make an upgrade button for it. How would you do that?

Basically, the way I do it works like this:

Make 2 custom units, intial and upgrade.

Then, I add the intial to the peon's structures built list.

Next, I add the upgraded unit to the intial unit's Trained units list.

Finally, I add a trigger. Once the player begins training a upgraded unit, I replace the intial with the ungraded.

Attached is an example.

You can also add building animations, birth, is the string for human towers. You can also do order the intial to start building the upgrade on it's old spot. There are more elegent ways. But I find these the simplest.

BTW - The Advanced Editor has some more powerful options which makes this a little simpler. But, I don't know it well enough. So, I'll leave that to the people that do.