Suggestions needed for Adjustable Snapping Tile Game

I'm looking to knock up a quick app for my nephew.

He's into building games such as minecraft (of course), Sims and Simcity and the Tycoon games.
He doesnt care much for NPCs its more the building and designing aspects he's into.

I'm looking at doing a grid mapped tile game where if two compatible tiles are placed next to each other they snap together for a new graphical representation, think old school Simcity with 2 houses becoming condos.

What I'm looking for is any suggestions as to what i should be looking at when it comes to Snapping Tile Mechanics.
The catch is this that it needs to have the option to do tile by tile placement with the auto-adjust for clicking and dragging different sizes.
I'm not talking about auto-filler I mean lets say this House Tile is 2x2 but he wants to make it 3x5 so the floors would need to be auto-fill but the roof and walls would need to expand with the drag much like how The Sims does when adjusting a houses size.

For starters its going to be a simple off tilt down view 2d app, but if he likes it I'll consider making it more explorative for him.

Any suggestion would be greatly appreciated.

 

at least 2d tools had basic example of auto-tiling like that,
https://docs.unity3d.com/Manual/Tilemap-ScriptableTiles-Example.html

 

Thanking you ill look it over.
Cheers