Sawmill - OSRS Wiki

A sawmill is a shop which also serves as a facility, and facilitates the creation of planks. The sawmill operator working there can turn four kinds of logs into planks for a fee, and also sells Construction supplies: saws, bolts of cloth, and three kinds of nails; they share the same stock. Players can have their logs converted to planks by using the sawmill operator's "Buy planks" option. He is able to create regular planks, oak planks, teak planks, and mahogany planks for the player assuming they have the requisite unnoted logs and enough coins.

Sawmill - OSRS Wiki

Sawmill operator - OSRS Wiki

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Sawmill agreement - OSRS Wiki

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What's the best way for me to get planks and is mahogany homes my best bet? Also what construction level do i need for most of the decent things in my house