The 1-2 tile constructions on the overview or worldmap in Renryuu are done with normal events, which appear once the switch for it is active. The change to the streets were a bit more difficult though, as they don't only affect the tile they're build on, but also tiles next to them in some cases. For example when a street goes through a forest, the forest tiles next to it is changed. That's why I made 2 copies of the worldmap for each possible upgrade of the streets. However, for the overview map, I use parallaxes as background image instead of a normal map, so everything is on one map instead of having to create several copies of events each time I make a change. In hindsight, I think the parallax method probably would've been better for the worldmap as well, instead of making multiple copies of a map.
Since you want to allow the player to built a town, things are a bit different, as you want to have several individual objects with multiple tiles to appear separately.
What exactly do you want the plugin to do? What kind of system are you looking for?
What the normal RPG Maker can do is to make a building out of multiple events, which all use the same switch to make it visible, and the building would be an image in the character folder, so that you can make the events look like that. It's also possible to "stretch" the size of the character image, which could be used to allow one event to display an entire house. However, the passability of the event would only be applied to that one tile of the event. Which means you might need to make multiple additional events to block the player from running through the house. (Putting a $ before the character sheet image name makes it a 3x4 set to the rpg maker, like the big gates of the default sets)
This image shows an example of what I mean. The purple background only serves to show the 3x4 tiles and would be transparent in the image you use in the game. The size of the image is so big, that one house can fit into one "tile". The placement of the house within these big tiles can be a bit tricky though, to make it fit to where you want it to be in the tile grid of the game.
Another possible solution is to use pictures. Pictures are images that are on a layer above all map tiles and characters. Normally they're on a fix position on your screen and don't move when you walk your character, but there are ways to make them stick to the map. To use images for the buildings, you'd need to add a global event to each entrance/exit to the area, to add/remove the pictures every time you enter/leave.
In the end, I think doing it with events is probably the easiest solution, at least based on what I imagine you want to do.
