I do agree with your strategy on working with the land, but it does not always work. It's good for smaller structures or hobbit-holes
it is custom build if you have to expand the island and re-teraform it later i actually built the house on the part where there is just water underneath if you took a potion of underwater breathing or had respiration helm you could go under it
All houses are custom built if you build them yourself, i built my house my way so its custom Sent from my House that is mine with my alive dog