Do materials get used when you start a construction in Die2Nite? Or, do they get used when you finish a construction?
Materials are not consumed until construction is finished. However, you can only do construction if all the necessary materials are present. This is often utilized to stop unwanted construction by having someone remove one of the necessary materials from the bank and hold on to it. AP that has been spent on construction of a building that no longer has the necessary materials is not lost, so once the materials are present you can pick up where you left off.