The combination of stone and core log supported with iron wood beams (need to be continuous from the ground contact) will let you build the highest without mods or spawned in artificial support.
A screen of a boathouse I built. Longship parked under a large building. It even has a stone fireplace upstairs.
https://steamuserimages-a.akamaihd.net/ugc/2053113256282784437/E6138848232F26CC2A8441CA53B24BCC481F79B4/?imw=5000&imh=5000&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false