Choose the location best-suited for your needs. A hunting cabin would seem out of place in the center of a field, while a playhouse would not be safe in the woods. Use your own discretion when choosing a location, but prepare for your cabin to be there permanently.
Choose materials that are appropriate for your needs and your climate. Wood is considered to be the most universal and traditional building material. You can get adequate materials for your project from local home improvement stores or construction suppliers. Even added touches like shingles, insulation and gutters are available at most home and garden stores.
Excavate your site, clearing it of all debris and trees or bushes. Since the cabin you are building will measure 12 x 16 feet, you'll need to make sure that you clear out an area equal to these measurements, oriented to your liking, plus an additional 4 to 8 feet for construction room.
Level your building area to make sure that your cabin will be stable. You'll want to use a construction level, tape measure and shovel to measure the site and add or subtract soil to make the site perfectly flat. Once you have a level site, use a tamping iron to pack the soil down as tight as possible.
Deliver your lumber to the site and make sure you have enough. If you're building directly on the ground, you'll want to use pressure-treated wood to make up the floor of the structure. It's recommended that you purchase four concrete "deck blocks" to create a gap between your cabin floor and the soil and help shape and maintain the frame of the foundation.
Construct a 12 x 16-foot frame for your floor using the pressure-treated wood and the joist brackets. Space the horizontal boards within the frame by about 16 inches, making sure that they are all vertical (thinnest side facing up and down). Measure and cut sheets of your 5/8-inch pressure-treated plywood board and nail them into the tops of the frame to create a floor.
Construct wall frames using 2 x 4 pieces of wood cut equally to your desired height for the cabin. Make sure that there is at least one "stud," or vertical 2 x 4, every 16 inches. Use joist brackets on 16-inch pieces of wood to connect the vertical studs. Nail together the frames, leaving space for windows and doors per your design.
Raise the frames for the walls and make sure they are vertically and horizontally level. Nail each to the floor frame, and then nail each wall together. Cover the outsides of this frame with cut plywood, minding the spaces you've left for windows, etc. Insert insulation before repeating this process on the inside to form interior walls if you're planning on insulating your cabin.
Create a simple roof by nailing joists to the studs that make up the top of the wall, and then spacing a series of boards every 16 inches just as you did for the floor.
Climb your ladder and begin nailing more sheets of plywood onto the ceiling frame to create a roof. Make sure that these sheets overhang the edges of the frame by at least 12 inches for drainage. You can also use additional pieces of wood to raise one side of the frame, creating a slant that will force rain to flow off to one side.
Use the tar paper or moisture-repellent fabric to cover the whole cabin, especially the roof. Nail it into place so that it creates a sturdy, solid-feeling wall. With this complete, you can create the actual aesthetic look of your cabin by covering it with stained wood, siding, shingles or even logs.
Decorate your new cabin. Add shingles to the roof, add fiberboard to the walls, install windows and doors, among other things. Your basic frame is complete. You can now add anything you want to improve the look and feel of your cabin. Leave it bare and stripped down if you want, or make it comfy and relaxing. From here on out, the design is up to you.