I was thinking about making a map, but a major part of it would be clouds. As in, it's a large floating island, and all around it would be clouds.
Or, there could be several islands, with clouds all around them, and you could travel between them.

What I want to know is in which terrain could I make something that looks like a cloud, and how would I do it?

Try pre-placed dark swarms.

Wouldn't they die in pretty quickly? Would that happen if you placed them as sprites?

Only "naturally" made Dark Swarms/Disruption Webs time out. The only problem I see is that A. they'd be orange ( 'course, for all I know, that could be a good thing ) and B. they'd be rather repetitive ( all identical clouds? >.> ) . Proper placement could mitigate B, if you don't need lots of "cloud"y area.
Though I do have to wonder how well using Disruption Webs, Dark Swarms, Pylon Auras, and possibly other spell effects would work... though then you're likely starting to be using bloody fucktons of sprites, which could hamper gameplay...

That's what I was wondering... Is it possible to use actual terrain to make it look like clouds?

Doubt it. You might be able to get Picture Mapper to do it, but I doubt that as well. Give it an image of a cloud (top/bottom view of one) and then see if you can downsize the result epicly. If you want to try, it's in the DLDB.

Picture Mapper only affects the minimap. It would have nothing, at all, to do with the way the tiles themselves look.

What I meant is, it might help you find tiles that work for clouds, because minimap tile color more or less corresponds to main map tile color. Emphesis on "might". VERY STRONG emphesis on "might".

No it doesn't TZ. If it looks really white on the minimap, it isn't necessarily an all white tile. It could be part of the bone doodad, but still not look all white, there are parts of dirt. As for the darkswarm idea, something to help negate the repetitiveness would be adding hallucination deaths here and there. The only other thing I can think of is modding to change how tiles look.

yeah im pretty sure there is no combo in any titlest that has somthing that resembles clouds. but i would definatly refer to the visual effects list to get what u need

An other way of doing so would be to create (or pre-place) buildings and either make them move around, either disable them so you get only shadows, which could be like the shadow of clouds that are way over the island.

This, and you can use different buildings for different types of clouds, or maybe use two buildings floating ontop of eachother for another type.

Issue with Dark Swarm is that it cannot be moved, you can make it last forever as long as you give it to a player other than 12, but you cannot move it, so it's a permanent placement, unless you just remove it.

I think your best best is the cloaked buildings idea, it might look kinda strange, but it's as good as it gets.

A long time ago I saw dark swarms under a ton of pylon auras.

The problem with this would be the sprite count. It would shoot up like a rocket through clouds...