A greenhouse is only as good as the decisions you make before you build it: the right size for your garden and the right glazing for your climate. Get those two things correct and you will grow year-round; get them wrong and you will fight heat, cold, and wasted space. Here is how to choose.
What size greenhouse do you need?
| Size | Best for |
|---|---|
| 6×8 | Seed starting, herbs, a few plants |
| 8×10 | A dedicated hobby gardener |
| 10×12 | Year-round growing with bench space (the sweet spot) |
| 12×16 and up | Big gardens, serious growers, small market operations |
As with sheds, most people wish they had built bigger. Benches, shelving, and grow beds fill a greenhouse fast, so if you are between two sizes, choose the larger one.
Which glazing is best?
- Twin-wall polycarbonate – the best all-rounder. It insulates far better than glass or film, diffuses light evenly so plants do not scorch, and resists hail. Ideal if you garden through winter.
- Glass – the most attractive and clearest, but the most expensive, heaviest, and most fragile.
- Greenhouse film – the cheapest way to get started, but it needs replacing every few years.
For most DIY builders in a real winter climate, twin-wall polycarbonate is the smart choice.
Orientation and ventilation
Run the long axis east to west so the broad side faces the sun and captures maximum winter light. Then plan ventilation: roof vents, side vents, or a louvered opening. More greenhouses lose plants to overheating than to cold, so airflow matters as much as sunlight. Add a thermometer and, if you can, an automatic vent opener.
A few extra tips
- Put the greenhouse where it gets full winter sun, away from shade cast by the house or trees.
- Include a solid, level foundation – a greenhouse racks and leaks if the base is not square.
- Plan for water access and, in cold climates, a small heat source for the coldest nights.
Ready to build?
Pick the biggest size you have room for, choose twin-wall glazing for winter growing, and orient it for light and airflow. See our roundup of the best greenhouse plans for 2026, our 10×12 wooden greenhouse plan, or read the full step-by-step guide to building a greenhouse.