I would like a raid with the boss as a green dragon that is similarly laid out like Tempest Spine (or not) maybe call it Lair of Poison.
I would like the lanscape to be something like the new quest in the Cerelean Hills mostly outdoor with a few small and large caves here and there. In route to the green dragon you might encounter some highwayman that really is not tied to the boss but in a way that makes sense to the quest.
This might be a dragon that is hunting and killing some small village occasionally for food and the like.
Some of the things you might encounter as well might be some wyverns and other dragon kind as well as some small green dragons that may be the green dragon's boss children or something. I would think that the boss green dragon be the eldest possible dragon in D&D and that this be a level 20 raid or higher if possible. Maybe as you trek to the eventual encounter you are traveling up various beaten' paths along some mountain both on the outside and occasional paths that lead through smaller caves and back out to a path on the outside of the mountain.
The Green dragon lair could be some extremely large cave with various minions that she would summon or that just reside there as well. Maybe one small dragon is in there not with his or her other borthers and sisters or something else be imaginative. In this cave lay vasts mounds of gold like in Gianthold Tor and a chest or two.
A pre-raid might be something that is not really tied into the boss but neccessary to gain access to the raid quest. Maybe the boss of the pre-raid is the eventual Sharn Sydicate boss or something similar that you have to beat just in order to get him to talk about the location of the green dragon lair. I believe not all pre-raids have to on the same story line as the raid.
What might be some ideas you have for a dungeon?