Hi
I have just built my greenhouse last summer and here are few tips
The base needs to be secured down with anchor type bolts b&q do these kits for less than a fiver you will have to dig out the ground level and then I used concrete at the 4 corners and middle where the holes are in the base and bolted it down.
I then I laid some concrete paving slabs down the middle for a path and used sand and then 10mm pea shingle for the sides to a depth of about 3 to 4 inch I would also lay some weed membrane down before you put the concrete frame, flags, and shingle as this will help to prevent weeds coming up in your greenhouse.
The glazing I have used polycarbonate because when I bought mine it was second hand and it was going to be cheaper also we have a grandson and I am thinking footballs etc so that’s up to you.
I have been using my greenhouse over the winter to grow my collection of south African bulbs so it has been heated I use a 500w oil filled radiator that has been quit cheap to run although an electric greenhouse heater would be better but then it will also cost more you could also get some greenhouse bubble wrap to insulate your greenhouse this is much thicker than parcel stuff and will help to retain heat and save on heater running costs has it as done for me
I would have liked an 8x6 but with space I am limited to a 6x6 but that’s been ample so far with staging etc you can create a lot of growing space.
Have a look at this link below this shows and explains how to do a base and foundation also they is a good book called The greenhouse expert by Dr DG Hessayon that is readily available from the internet
http://www.lets-do-diy.com/Projects-and-advice/Garden/Building-a-greenhouse.aspx
Steve

Hi Donna. Well, that's a very comprehensive answer from Steve. I would just add that as soon as you have a greenhouse, you'll want a bigger one! So I'd go for at least an 8' x 6'. We bought a lovely cedarwood one from Alton (using a small inheritance from my Mum - to remember her love of gardening). It seems to stay warmer than our previous aluminium one . . . no heater, but it gets sun all day. Fine for starting off seeds - good luck, and hope you get one soon - you'll love it!

just blogged my greenhouse if you want a peek. I understand you are looking for new but this could be useful info for other's wanting to go down the 2nd hand route.
I layed out the ground exactly the way Steveg has mentioned, concrete slab path down the middle, gravel either side all on top of membrane, trouble free & long term use.
Also Sheila has mentioned going for an 8x6, I also decided a 6x6 was going to limit my growing space so went larger but 6x6 is so useful as staging & shelving are all available as Steveg mentioned to increase growing area if space is limited.
Goodluck Donna & we're sure OH is going to be extra generous as it's your birthday present & please send us the photo's of your progress & first plantings.

Hi Donna, Agree with all above, there's some pictures in my photo's , might give you an idea how to lay it out. Go for the biggest one you can fit in, because as Sheila say's , once you have one its never big enough. I started with 1, I now have 2. Believe me, you won't be stopping at tomatoes! Best of luck.

Donna, I've just found a previouse reply I gave a while back re. Greenhouse. Hope it helps.

Ive got 2 greenhouses and I put them up both the same as each other. The first thing I done was put the base of the GH together, so you know exactly where the GH is going to be sited. I then marked out , with a shovel line around the base, allowing 4ins each side, IE. 8ins wide. I then dug out a trench where the base is going to go according to these marks, about 4ins deep, but this could vary if the ground is sloping from one side to the other. Smash some hardcore up or stones etc and put it in the trench. If you are laying a membrane place this on top of the hardcore. Lay concrete breeze blocks on their sides, spacing out about 2 -3 ins apart. Level up from corner to corner, and set in concrete inside and out side of blocks. Make sure you place the base of GH on top of blocks before setting concrete, so it fits OK.
When this is setting you can put the GH up separately and loosely bolt together.
Go and have a cup of tea and get a good nights rest.
Lay the base of GH on the now set block base and fix the GH to it. Use minimum 2ins screws, raw plugs. You will need help with putting the GH up. Once fixed loosely drill the base into concrete blocks and fix securely, tighten up all the nuts for GH.
I will put a picture of mine on my page , so that you can see how I finished the inside .
Concrete blocks £1 - £2 each B&Q
Sand and cement , couple of bags sand, 1 cement, approx £10
It is really worth taking time to make sure you get it fixed down securely, its got to last.

I´ll be following this question wih a lot of interest as my new green house was delivered last week and is still in its boxes in the shed, it is only a very small one, 6 X 3, so very small, the one thing that is giving me a slight headache is the base, in the building instructions it said that a wooden base would be enough for it and eventually put paving stones end up to stop it blowing away in the wind, although where it will be erected it is sheltered from winds, another idea is to buy "earth screws"...they are like big cork screws and that should hold it firmly enough. As I said I will be watching this so as to get some more ideas.

It's best to site your Greenhouse North to South with the door South and roof vents East and West. Rogi, to save mixing concrete with the fear of not getting the base level, you could use 2 concrete fence spurs placed on a membrane. The bolt hole in the spurs will give you a fixing to the frame. Fill the floor area with pea shingle, concrete fence posts can be used for larger greenhouses.

And I see no reason for you to heat given the use you are going to put the greenhouse too :-)

You should definitely get a greenhouse that you can grow into, Donna. There are budget greenhouses that go up to about 8' x 6', then there is a price break and larger ones become much more expensive. Our second greenhouse was an 8x6 from B&Q.
I prefer glass for the glazing but if breakage is a real concern then use polycarbonate.
It would be much too expensive to try and heat the whole greenhouse. If you are going to raise your own toms from seed then buy an electrically heated propagator or raise them on the windowsill. For the few that you are going to grow I would buy plants in.

Wow, so much to take in!! Thanks for all your advice.

Your welcome - have fun!