Does it not start to become cheaper to rent some storage and buy the items when they are low, like timber now and then the other core bits, biding your time. Though storage costs a factor and equally equity to buy the materials over time at the right prices. But then those materials are assets and if you buy cheap, even if you don't go ahead - resell will break you even at least.
Much the same way air-con units and fans cost more in the summer compared to winter - prices do seasonally fluctuate and those can have a knock on effect. So cheap timber will drive up the other items with demand, so you can almost foresee once timber goes up, the ancillary items will come down due to demand again. That and winter, will curtail some demand and that may well be the time for buying some items.
Much the same way air-con units and fans cost more in the summer compared to winter - prices do seasonally fluctuate and those can have a knock on effect. So cheap timber will drive up the other items with demand, so you can almost foresee once timber goes up, the ancillary items will come down due to demand again. That and winter, will curtail some demand and that may well be the time for buying some items.