13 Cheap DIY Greenhouse Plans Greenhouses are great to have for so many reasons. They extend the growing season in cold climates and can allow you to grow varieties of plants you may not otherwise be able to grow in your area. They are perfect for starting seeds and can provide a nice little calming retreat. Large or small, building a greenhouse doesn’t have to break the bank. Here are 13 inexpensive DIY greenhouse ideas that include plans or tutorials..