How would you do this? Encounter on two levels.

[Oladahn]

So the very first encounter in the campaign I'm writing involves the PCs entering the area and being shot at by archers from the top of a guard tower. I can't have the map as just a 20' square top of the tower as that would be a bit of a giveaway as to what's happening and where the attack is coming from.

So my cheats way of doing this is to have all the action take place on the ground floor map but keep the archers invisible and, when the pc's eventually break down the tower door, delete the archers and start a fresh encounter.

Is there a more elegant way. perhaps involving layers?

[LordEntrails]

Not sure of the layout etc, but if you can put the upper level on the same image and just off to the side them you don't have to worry about moving tokens between maps. Also, though I generally don't like them, an isometric map can work wonders in this situation (but Masking and LOS may not be usable).

You should be able to do this with layers too, but are going to have to be careful and play with it. I haven't done that yet.

[GavinRuneblade]

I use two maps for things like this pretty often, it works fine. One for each floor. I've also done it when I have encounters happening in two places (queue song "don't you know you never split the party...").

Sometimes they can see both maps at the start, sometimes not.

[Speculi]

..., when the pc's eventually break down the tower door, delete the archers and start a fresh encounter.
Why delete the archers? You can keep them on the CT and move you player tokens to the new map, when they reach the top/inside of the tower. The Archers can already be setup on the map for the top floor. But maybe one of your PCs finds a way to get there earlier than the other? Teleport, Fly... whatever is possible. Or they can already affect them in a way (magic, grenades, homing missile, just shoot back).

If there is nothing else on the ground floor to do besides breaking down the door you could also just keep that part as "theatre of the mind". Depends on how "tactical" you want to approach this.

For the general approach, I would also either go with multiple maps for each floor (could be just ground and top) or one bigger map, containing each floor as sections next to each other and hide those they can't reach yet.

[Oladahn]

Thanks all. I eventually decided to go with my original solution and to implement your suggestions in a future scenario.

Many thanks for the help.