The 1 x 6 and 1 x 8 boards should be kiln-dried, finished lumber. If you are making a large number of kits, the plywood option might be cheaper depending on where you live. The wire is used to make a loop that is used to hang the house. Farmers would use baling wire or electric fence wire to make this loop, but most urban people will not be able to buy such a thing in small quantities. So look for single-stranded copper or steel wire that is perhaps 16 or 18 gauge.
Picture hanging wire is a reasonable substitute.
Each kit consists of a roof, a floor, a front door, a back and two sides. The two sides and the back are 12-inch long pieces of 1 x 6. The roof is an 8-inch long piece of 1 x 8. The door is an 11.5 inch piece of 1 x 6 ripped down to 4 inches wide. The floor is a 4.5-inch piece of 1 x 6 also ripped down to 4 inches wide.