Upgrade path

Plywood Osb Center Plate→ 4× Wood →Window Plug 03→ 10× Cobblestone Rocks →Cobblestone Block→ 10× Concrete Mix →Concrete Block→ 10× Forged Steel →Steel Block

Hit a placed block with a stone axe, claw hammer or nail gun while carrying the material of the next step: 4 hits per upgrade.

Where to find (9 POIs)

Flushing Rule Palace (tier 4), Mason Farms (tier 3), Pop's Pawn & Bel's Bakery (tier 3), Navezgane Creamery (tier 2), Pass-N-Gas Store #03 (tier 1), Rifle Martyrs (tier 1), The Clutter Chest, The Joelton Hotel, The MeMaw Residence.

Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.