tile based systems, pathfinding and building setting can all be handled by aaron's A* pathfinding solution. You can find some actions for it in the new actions section here in the forums. I'll likely release a new update this weekend, but it will be backwards compatible, so you can just start testing with the old package and then just update later.
The Grid based system uses nodes of a certain size which save whether a certain coordinate in the game is walkable or not. So if you say every node has only 4 connections to nearby nodes, and set the node size to something larger, you end up with a tile system which can also be used in pathfinding.
building setting can be done with the IsNodeWalkable action, and the IsPathPossible actions in a TD.
In a strategy game you likely want buildings which are larger than one node, so there you can use the area node walkable action.
Play around with it and then ask specific questions. I've been through pretty much all of it but it would be a very long post if I tried to explain how to do ALL of it.
EDIT: right now the rts is not really in a showable state. I can show it to you in a few hours when I've fixed the lighting.
