When we moved to this suburban house in 2001, there were countless repairs starting from the roof down to the fence. It was a learning stage for us since we were not used to hiring people to do such repairs. And in the process of the continual house repairs, we learned that carpenters, masons and other repairmen has the penchant for buying excess materials. We are always left with extra hollow blocks, galvanized sheets, sacks of cement, etc. After years of such experience, my husband had learned to double check the estimated count of the needed materials for the house repairs. There was even a time when the worker argued with my husband why he listed 50 hollow blocks when only 20 were needed.... the 30 was allowance for breakage, huh. That's the style of the workers here.
I generally cut things pretty close when I build but I am also the one doing the planning, buying and building. One thing to note is the big question: Who does your plans? Normally, architects and drawing people do not take material lengths and sizes into account. As an example, if a plate or shoe is supposed to be 13' 6" then the builder has to use either a 16' 2x4 and cut it down which leaves 2 1/2' as potential waste or add 3'6" to a 10' piece which means cutting into something else. Cuts mean potential waste and it takes a good planner and builder to limit it but there is still going to be waste which means that everything on the burn pile is paid for and paid for by the foot. In my area, if there is a 6" 2x4 block on the waste pile it should be considered to be about 30 cents on the pile which is why when I plan the cost I plan on another 10% above the basic figure. Now, concrete blocks are a whole different animal. Unless you are using a block saw and two bar centers on the block then you're gonna have a whole lot of waste. Normally, block layers do not have block saws and even if they do the buyers do not buy two bar centers because they cost too much. The solution to that would be to buy half blocks but again, if you don't have a good math guy who knows how to calculate the number of halves needed then you're pretty much stuck busting whole blocks to make halves which is a whole lot of waste especially if the plans aren't exact which take into account the dimensions of whole blocks and the mortar in between them. If the plans can be stretched to accommodate whole blocks throughout the project so be it. But, that is hardly ever the case and there winds up being a whole lot of block pieces in the open cells because normal blocks do NOT make 2 good halves. (though I have seen it tried but do not trust the construction) Mortar mix is another one that can't really be estimated accurately. But, even if you could get it down to the last pound in a good estimation the question remains as to whether it is cheaper to buy the stuff by the pallet or by the bag. If I can get a much better price by buying by the pallet on a larger project then so be it. A couple of extra bags at the end will definitely go on to another project and if kept dry will last forever while waiting for that extra endeavor. Hope it helps.