Wood is a traditional building material. You should not spend money on expensive timber for outbuildings, you can use a convenient building material - sleepers. They do not require additional processing before work and are much cheaper than other wood.
pine or impregnated sleepers, screws, bricks for laying the foundation of a house, metal brackets and bolts, metal pins, steel strip, glass wool, level, plumb line
Match sleepers of the same size. Mark the length of the sleepers so that they fit snugly together in each row at the joints. Place a waterproofing layer between the foundation and the first row. Lay the first row of sleepers flat and bolt them to the foundation at a distance of 1 m from each other. Erect the walls of the house from the sleepers, fastening the subsequent rows of sleepers to each other with metal brackets, and the rows to each other with metal pins. Lay all sleepers flat. Check the joints between the rows of sleepers. The boundaries of the second row should close with the first row, and all subsequent ones should be on the same level with it. Align the sleepers along the inside of the wall with level and plumb line.
Fasten the corner sleepers through 3 rows of crowns with metal squares. Ensure that the building is kept warm. Seal gaps between the foundation and 1 row of sleepers with tow or glass wool. Seal gaps between all rows of sleepers. Run a strong steel strip diagonally across each of the four walls to provide rigidity. To do this, drill holes for screws on a steel strip (30 mm wide and 4 mm thick). Mark the holes so that they are in the middle of the sleeper.
Carry out interior wall decoration. Sheathe the inner side of the sleepers with waterproofing material that does not allow creosote evaporation. Use roofing paper, polyethylene or masonry mesh for this. Sew up the walls of the sleepers with shingles and plaster or sew up with drywall and putty. Wait for the walls to dry and start painting or wallpapering them. For the exterior of a sleeper structure, use vinyl or metal siding. It will hide the protrusions of the walls, the unattractive color of the material and will allow the impregnation to weather out.