There are many people who think about starting a greenhouse, but few actually take the time and energy to put thoughts into action.
So, get a plan, and get with it. Don't worry about making mistakes along the way. That is how many of us learn.
Do you want raised beds in your greenhouse?
Or do you want to plant everything in pots?
Having a closed greenhouse means you are in control of all the environment. Pests and diseases, warmth and humidity, must be controlled and you must water your plants on a daily basis.
Having an ample supply of good quality water is essential. Some catch water from run off of building and recyle it in their greenhouse, while others use well water, reservior water and even city water.
I am fortunate in that I have a pond on a hillside above my house and use gravity to pull the water down to my greenhouse.
Adding significant heat and light may be required, if you have a winter production of warm loving vegetables.
It also requires a good quality soil source. Contact other nurseries in your area and find out where they buy good quailty soil. You will want to buy two or three cubic tons of soil to get you started.
Now, just think about it, You are in control of every living thing inside of your greenhouse.
You must also have a pollination process, such as honeybees, bumblebees or artificial pollination.
Begin collecting containers such as two-liter plastic coke bottles that you can cut in half and punch a couple of holes in the bottom for drainage. Any old contain will work. You can even start plants by making newpaper pots.