Greenhouse width/length?

Complete greenhouse newbie! We are fortunate to have space to put a greenhouse, if we remove some raised beds. We were thinking 10ft x 12ft, but this could vary by width and length up to 20ft long. Are there any considerations if we went for say 8ft vs 10 or 12 wide? Obviously its wider, but is there an 'ultimate' width in terms of practicality/paths vs growing space etc?

 

I suppose it depends what you want to grow?
How many tomatoes, chillis, cucumbers can you use?
Do you want to overwinter tender plants in there, if so lots or a few?
How much space do you want for seeds and young plants in spring.
I would go for 12 ft wide.
Also how much do you want to spend?

 

Slightly the opposite to @NigelJ! Years ago I put the same question on GC. I am lucky and could afford to get a big greenhouse having the space and was treating myself having given up the dreaded cigarettes!
A very knowledgeable gardener enquired as to whether I was an Orangutan as I had said I was thinking about getting a 12ft x 12 ft greenhouse. For me he was spot on that I should go for length and not so much width. I bought an 8ft x20ft Rhino greenhouse. I then put a 2ft wide path down the middle and have 3ft beds either side of the path.This suits me and it is usually stuffed with tomatoes peppers chillis cucumbers sweetcorn etc etc. of course as everybody who has a greenhouse will admit it is not big enough. All I would say is go for the biggest you can afford as you will fill it!
This is mine after I have taken up every available inch for a charity sale I run annually.

 

I agree with @hailbopp . I got a 20 by 8 Rhino as well. The staging on either side is not too wide to reach plants at the back. I also had it with an interior partition so that I could heat a smaller section

 

I have a 12 x 12 with staging down either side, then a narrow path with a wide space between the two paths. The staging is full of plants, at the moments chillis, bell peppers, basil, some dahlias, salvias and nerines. The central space is full of tomatoes, cucumbers, a melon, some more dahlias, and a number of odds and ends of plants that don't do well in my summers.
By the end of October, there will be pots of freesias, a load of stuff that's not quite hardy and definitely don't like my wet winters. Then there's a number of rooted cuttings and a variety of seeds some germinated, some germinating.