At some point in your game (usually inside a Common Event), you open the build menu with a plugin command (MZ) or a script call (MV) like this:
MK.Sandbox.openBuildMenu('houses')Now, only blueprints with the category "houses" are shown.
For the other question: Unfortunately, the source map must have the same tileset as the current map. RPG Maker doesn't support mixing tilesets well.

