Before you build your hot house, design it on paper. A good-sized hot house is generally about 8 feet by 10 feet, which leaves plenty of space for shelves and hanging plants.
Purchase the building materials you need. A basic hot house uses a 2-by-4 frame with a fiberglass or plastic covering. Based on the dimensions of your hot house, determine the approximate number of 2-by-4s and the amount of covering you'll need.
Build the hot house walls by nailing 2-by-4s into four identical rectangular shapes. For support, nail one 2-by-4 vertically in the center of each rectangular wall.
Screw your wall sections together with metal braces after you've propped them into place.
Leave room for a door on one side of your the hot house. A door should be about 2 feet by 6 feet. Insert two 2-by-4s on either side of the door. Later you will attach a door with hinges to one side of the door opening.
Build the hot house roof by nailing 2-by-4s together that are the same size as the footprint of the hot house. Support the roof by placing one or two 2-by-4s in the center of it. Cover the roof with the fiberglass or clear plastic covering and attach hinges to one end, which will in turn connect to one end of the hot house. Put the roof on the hot house and then secure the hinges to the frame.
Cover the rest of your hot house with the fiberglass or plastic.
Make a door out of 2-by-4s and cover it with fiberglass or plastic. Attach it to the door opening you created on the frame.
Add a heat source for your plants. You can used a space heater, kerosene heater, solar heater or any other heat source you can come up with. Also install a fan to facilitate air circulation and cool the hot house on warmer days.
When using electrical devices in your hot house make sure to take the proper precautions to insulate, secure and protect all associated wires. As the wires will be exposed to heat, moisture and other weather-related elements, they can present a safety liability. If you don't feel comfortable adding electricity to your hot house you can try and keep it hot and well-circulated in other ways, such as using mirrors to reflect the sunlight and creating lots of opportunities for drafts and breezes to enter the hot house.
Put a thermometer in a shady part of the hot house to help monitor the temperature.