Contemporary kit and fully built houses are typically made of plywood or medium-density fiberboard (MDF). Tab-and-slot kits use a thinner plywood and are held together by a system of tabs and slots (plus glue). These houses are usually light-weight and lower cost but often require siding, shingles, or other exterior treatments to look realistic. Kits made from heavier plywood or MDF are held together with nails and glue.