I Want to Make this Building. Where do I start?

[Sumpter250]

That is an interesting structure! My friend's Dad owned the boat yard at the end of the street we lived on. Their house's foundation was an old wood barge set up on concrete blocks. Looks like the double doors at the "stairway end" are the only large doors......hope they're building a small sail boat in there. :o
Northeast scale clapboard siding, 6" ( .068" ), or even 8" ( .092" ) would work for HO, unless you intend to lay in each board, then I'd say .010" X .080" stripwood, with a scale 2" overlap.
Is that really board and batten roofing ???!!!! ( you can get that in 24" long sheets too, or just lay the battens on after )