Greenhouse Decision

Can anyone help me please?  I have bombarded myself with greenhouse info from the web and am now totally confused.  I only have room for a 6x6 or 6 x 4ft one but do I get glass or plastic, twinwall or single.  I am minded to get plastic as I have dogs that like to romp in the garden but am then afraid it will take off in the next gale!  I have even looked at geodesic domes but the smallest viable size is 3m really and expensive too - I also quite like the idea of constructing my own...saw one made of posts and hoops and corrugated plastic once in a gardening mag...but can I find it now.
I only want it so I can raise my seedlings for the alloment and maybe grow a tomato or too.  I would be interested to hear what you lot have done and whether you found an ideal solution?

Thanks Stompy - appreciate your thoughts... should be out on the plot now but stuck in the office all day having to earn money instead of growing food!

I agree with stompy, glass for sure without a doubt. Aluminum is easy to clean and practical.
Having said that, I do prefer the look of wood.

I have 2 greenhouse in my garden. One alluminum with pollycarb (bought) and one ceder with glass (given).

The pollycarb is 8x4 and i thought was just right for me starting out. Until it got windy that is! The pollycarb keeps bowing out! It has cost just as much reparing it than it cost in the first place. Blowing a gale today and have lost a panel that was replaced only 2 weeks ago. Gutted. My neighbour has a larger pollycarb greenhouse that they got from B&Q, completely different from mine, and this to keeps losing panels and has done today.

Now the wooden is 8x6 and is swaying a little in the wind but looks solid. It also survived the winter winds too. We broke a pane while bringing it home so had to go buy another. Glass we have found is so much cheaper than pollycarb sheets!

Something else to think about. Not sure if pollycarb is recycleable but glass most certainly is!