WoW-ish Frostbolt.

Okay, this is what I made really quick to mess around. Still pretty nub at triggering atm. I'm not sure if the spell will cause any memory leak.
One thing is for sure that, it only works if there is only 1 instance of the caster in the entire map heh.

If you hold the Alt key, you can see the cast bar progressing.

There are a few problems I face now: the spell cannot be cancelled, is it hardcoded? The castbar unit can be selected, but if I give it Locust ability, I will not be able to see its health bar. :/ The 'cast bar' only appears when you hold the Alt key, I kinda want it to appear to the player even without holding the Alt key.

Anyways, check it out :P.

to simulate a cast bar, i would use floating text and the | charicter.

It can be cancelled; you have to order the unit to stop first. I'm not sure how to get around it because I don't think the unit can recieve any orders other than 'stop' while it's casting.

I think I'd go with Earth-Fury's suggestion for the casting bar. If not, you could give the progress bar unit a expiration timer so if they do select it they see the time left, but it's up to you if you think it detracts from the effect.

Also, you seem really interested, so I suggest you look at the JASS tutorials around the forum; I'm not sure how much you know already, but unless you're really set on doing everything in the GUI, it would probably make things much easier and faster for you as well as provide links to other useful resources.

Just a random idea if you don't mind using dummy units to cast spells, but you can make a channeling spell that does nothing, and when the triggered event of finished channeling happens you can spawn the dummy unit, shoot the frost bolt, and deduct the mana from triggering player.

Was thinking you might be able to do a swap ability too, make a frost nova channel spell that does nothing and costs nothing, then on the event you disable it then enable the frost nova one that shoots the bolt and costs the mana, issue the order of triggering unit to cast it, then swap the enabled disabled powers back.