I've been thinking about virtual architecture. Well, virtual everything, actually. But architecture is a clear example. Here's a strange, fun-filled fact:
Height and size are worth quite a bit less in a virtual world than a real one. There are two reasons for this. First, there are usually a lot more very large-scale structures. If every building is cathedral-sized, then cathedral-sized buildings just aren't very impressive. Second, most virtual worlds allow you to fly, or at least move very fast. And size is relative to position (fliers see everything as "shorter") and speed (a mile isn't very long if you're moving at 60mph).
This means that the "really impressive building" you've got planned is really not going to be very impressive after all.
But there's a lot of nifty tricksies you can use to fool your visitors into thinking your building is very impressive! Here's a few tips for the "inside" of your building:
The easiest is the design of the entrances/pathways. If the player is forced to progress in a specific way (through a door, under a ledge, down a corridor, whatever), then you know precisely where that avatar will be upon entering that area. You can use this to maximize the impact of a room.
For example, forcing a player to enter a building near the ground rather than having an "air entrance" will mean the player will be moving slowly and seeing the full scope of the room, rather than moving quickly and seeing it from halfway. If your building is suitably airy, the players will get hit by the full scope of it.
Another trick is "inhuman ratios". Most rooms are wider than they are tall. You can use this in your rooms. If you must have an "air entrance", don't lead into a normal-ratio room. Make the entrance itself the room: a very tall and comparatively slender "tube". Or make it lead into an extremely wide, deep, but short room. this can be enhanced with partial visual blocks - like columns or occasional plants - to give a very clear reference for distance. If you want your room to look bigger than it is, make these visual blocks smaller the further they are from the door. This should trick the eye into believing there is a significant distance between them and their larger brethren.
If you're thinking of how to make the outside of your building more alluring, that's pretty simple while being quite complex. In real life, the outsides of buildings are rarely intended for use. They are nothing more than barriers to keep out the weather. In a virtual world, there is almost never any need for that. Ideally, visitors can't tell when they've "left" the "outside" for the "inside".
This means you want to have an airy, open feeling. First step: vary the height of your outside areas/rooms. "Draw" in height variations and unusual floor patterns. Think "skatepark meets Victorian garden meets crop circles". For example, a waterway cutting through your building, or a "path" suspended over (or under) the normal floor. This height differential also serves our next point:
You can build a structure without roofs or walls, but it'll just be a park. Perhaps a park is what you're aiming for, but when the player can fly, a park has to be pretty freaking impressive to draw the player down out of the sky for things he can clearly see while up there. What you need are areas which the player (A) cannot see inside while flying, (B) are clearly there, and (C) have an inviting opening.
The simplest one is an "eaves room". This can be built underneath a raised portion of the "park", if you like. It is essentially a cave, preferably with lights or markings on the floor to draw the eye.
What constitutes an "inviting opening" depends on the circumstances, and is perhaps the most critical part of constructing your building. An inviting opening has to be something which the player could swoop through at full speed, if they were feeling adventurous. This means that if you're appealing to flying players, the inviting opening has to be quite large... but if you're appealing to someone who's already sauntering through the area, it can be barely large enough to squeeze through. Sauntering is much slower than flying.
Certain shapes appeal more than others. The stereotypical "door" is a wholly uninviting entrance, especially in a virtual world where stopping to let a door open (or, worse, opening it yourself) is an irritation outside the norm. Most attractive entries are tall and wide enough that the player won't feel any danger of "hitting the edge" while moving at their current speed. They also denote that they are entries by clearly displaying that the room they lead to is different from the outside.
To people on the ground, this is pretty easy: they can see the room. Whatever is in the room is a lure, whether that's toys or darkness or a sudden turn that looks mysterious. If the player is walking, the height of the door just needs to be significantly taller than the player. Width is actually a priority, because the player can move around on that axis, but not up or down.
In the air, however, nothing is quite as easy. A "tall" entrance looks quite short when viewed from a 70 degree angle from above. This means that air entrances are generally "sloped" such that someone looking at it from, say, 60 degrees sees an entrance which is decently tall. This can be as simple as removing a chunk of the corner of your building - commonly, air entrances are invitations to land and enter, rather than keep flying while inside.
Also, effective entrances (ground or air) are often "wedge" or "scoop" shaped.
It is very much an art to create these kinds of interesting openings. When combined with careful external mapping and internal flow control, you can have a building perfectly suited to the virtual world.
The key is to "re-scale" the experience of the visitors. What scale you want to end on in any given place is up to you, but there's a transition to be made. That transition is made primarily through entryways, whether your entryway is as simple as a half-shell over a table or whether it's as complex as a tall shaft leading to a short room.
Decide what you want to re-scale to. If you keep your players flying, they will have a hard time "settling down" and probably won't be able to socialize effectively. If your room is "short" (too short to easily fly in) then they won't be able to scout around to find a group they want to hang out with. A tiered or stepped approach is often very effective at allowing socialization while still drawing people down into a sociable scale of space, often with extremely limited "roofs" which give the impression of cover without actually stopping anyone from going through.
Shopping is quite different, of course, and buildings of that nature will naturally tend towards other shapes that force the player to see the products. Low rooms or, if flight is a priority, narrowish tubes/floating displays. This is a much smaller scale of space than the open socialization of last paragraph.
Of course, if you're building your structure to lure people in to explore it, then leaving it flight-scale in most places is just fine. It will naturally let people skip from interesting place to interesting place while never making them feel claustrophobic.
It's all about your priorities.
Anyhow, I hope this was interesting for you. Virtual architecture is a hobby. :)