For the Ghost Building/Area for this gen...(if it's still focused on a tropical plot):
The building should be a tower, similar to the past generations, which is spoken about by tribal people and shamans, warning people not to enter into it's haunted walls. When the main character hears that (enter bad guy's name here) wants to turn the building into a (enter syndicate name here) headquarters, he has no choice but to go mess up their evil plan. (Bad wording, but this is just a rough idea. >.>)
The building would have three floors:
1st: Two or three members of the enemy group, no wild pokemon encounters (as usual on the first floor...Or maybe that was just first gen, I can't seem to remember.).
2nd: A double battle situation where you have to walk between the two people where one is waiting above and one is waiting below, and another enemy trainer. Wild pokemon encounters can be found on the second and third floors.
3rd: (Staggered like the first gen top floor) Three trainers, and then at the top there should be some sort of leader. Not sure whether there will be three (or some other number) of peon-esque people such as the 4th generation, but some sort trainer who is stronger than the last nine(ish) people you just knocked out.
Some sort of reward relevant to the story should be added, such as the PokeFlute in 1st gen, The Red or Blue orb in 3rd, ect.
Pokemon wise, there should be a new duo of pokemon. But this time, I think it should be ZOMBIES instead of the average ghost. While the ghost generally get more human like in shape, I think that there should be a Zombie, who is more human shaped than the last.
Whether or not it should be an entirely new type, or if we make use of the ??? type, or keep it just plain ghost is open for ideas, but I just thought that we should have a more Zombie like pokemon, seeing as they've steadily been working up to it if you look at the final forms of previous pokemon.
Gengar: Arms and legs, stands on two feet. Eyes, nose, mouth.
Misdreavus: Looks like the head of a woman, and once it evolves it seems to be a bit more human like.
Banette and Dusclops: Look pretty human like to me.
Drifblim: Got away from the human look, but I think we should stick with it for 5th gen.
Now, the Zombies (should they be made into a new class, or use the ???) won't be transparent like ghosts. They will be solid pokemon, thus are able to be hit by normal and fighting type. If decided that they should be ghosts, then obviously they will pick up the traits of ghost type pokemon.
Possible Zombie traits:
Low Speed. For somewhat obvious reasons.
Weak to Fire and Ice.
Strong against Dark, and possibly Ghost or Psychic.
And...That's about all I have up to this point. Ideas?