Be sure you make it high enough and strong enough for hanging pots.
The first thing that I would buy is a watering wand, get the one that is about 3 foot long, and comes with a water bubbler nozzle, as it won’t wash all the dirt out of the pots and mess with the roots, they will cost $20. and are worth every penny, as with them you stand straight and just point it at the object waiting for water, I use mine in the yard and the greenhouse.
I think my last one came from K-Mart, Walmart should have them, think they are called a watering wand, but don’t get the cute little ones that are a foot long, go for the longer one and it is about a half inch diameter aluminum tube.
Yes, you should be able to work with your area.
Be sure it is tall as you can safely make it, at least house roof height to the eaves.
When you build, you may want to consider making it strong enough to cover later with fiberglass, as glass windows or insets gets too heavy and the glass always gets broken.
You won’t have the sun that you need for some of the summer crops, but with experimenting, will find a lot of plants that will grow in there.
The last big growing attack that came on me, I grew from seed tomatoes, peppers, lettuce, several greens and chard, in a room with north windows and smaller east windows and they all produced fine and in the gallon pots the tomatoes grew 6 foot tall. It was a wonderful jungle, only room to get to the plants to water them, it was in the next room to the wood stove, so got extra heat.
I cannot even grow in pots now, due to health, but you never loose the desire to do so.
If you screen it in, watch for a sale on rolls of plastic, it isn’t impossible to tack it up in the winter and that will give you heat in the house.
If you buy rolls of plastic, and plan to use it year round, it has to have a blocker in it that blocks the ultra violet rays, and I may have the name wrong, but it keeps it from falling apart in the sun.
But for one winters use, just get the $5.00 rolls of plastic at wallmart that is sold for ‘painter’s drop cloths’ called Plastic Sheeting, it comes in a 10 x 25 foot roll and is 3.5 mil thick....
Yes, I cheated and looked at the cover on the roll that I have.
Go ahead and put in a row of benches, the wooden pallets that things get shipped on, will be about right, take them apart and use the 2 x4’ center supports for legs and put the flat boards up for the table top, be sure to leave a half inch opening between the boards for the water to drain off and the air to circulate.
You will have problems that are beyond my knowledge, lots of rain, all I can think is that plants get in trouble when water drips in the pot and on them, or drown if it lasts long enough.
Here in Arizona, rain is a cuss word, my old roof has dried out and has leaks the repairmen have not found the source of in 30 years.
You will want to start your seeds 6 weeks to 2 months before they go out doors.Since it will be so long, put doors in both ends and if possible a vent/opening in the center roof.
Do it, you will enjoy it and working with plants is always healing.
If you put the bench against the house, leave a wide walk way, for you will soon have it filled with the 5 gallon and 1 gallon pots.
Start saving your coffee cans, the plastic ones, take outdoors and next time you barb-q heat an old screw driver or ? and melt 4 or 5 holes in the bottom and you have free pots that will grow a lot of the plants, free.
My family comes here every spring and cannot understand my still saving things that I cannot use, but how can I just toss things like coffee cans, when they are at the least flower pots and could be food storage containers.
If you belong to the Free Cycle groups, after you give something away, you can ask for what you need and it amazes me at the requests and thank you’s that I see posted.
I joined to see what it is all about, and as I can no longer drive or go out, I have not taken part in it, but find it interesting and have been tempted to respond.
If people give away building materials here, a poor area, then your area must be full of the things you need for your greenhouse, the screen is going to cost the dollars.
I can only give you my thoughts, for what they are worth, or as a friend often did to me, offer what I considered impossible solutions to the problem, and when I said ‘no way’, she would say “ok, we know what you won’t do, now what did you have in mind?”
Have fun.