Gardman 4-Tier Mini Greenhouse
If you have just a little room, the Gardman 4-Tier Mini Greenhouse
This size is best for starting seeds, and is somewhat limited in use for full size plants. This means you can get a head start on your garden even if you plant your young plants in the ground once they get started.
The plastic cover is removeable and zippered, to make it easy to put in or remove your plants. The plastic allows sunlight in while retaining heat to help your small plants grow. For those in colder climates, it includes a fleece cover to protect young plants from those cold nights.
You can secure the shelves to the posts with cable ties to make them even more secure. You may need to be a little careful with this in windy weather.
The Gardman 4-Tier Mini Greenhouse is small enough that you can keep it indoors if the weather isn't good enough to have it outside. The more mechanically inclined can even set it up on a little cart with caster wheels to have a truly mobile mini greenhouse.