I use First Tunnels, they have a good website that has films on showing how to assemble the different types. You can also build your own to what you need from there different designs and accessories .I would also go for the biggest you can as they are easily filled and check planning if you want a biggy. In my Authority planning depends on distance from other properties, in a field or garden, size etc. So mine is a 35 x 15 the biggest I can have in my garden at the distance from the road, any nearer the road I would need planning. Also field or garden means business or domestic for planning. The preperation is the hard work the poly themselves are reasonably easy. Mine took two folk to build. The polythene going on is easier than it looks because as you pull it over it sort of vacuums itself into shape so that gives you time to fix it without panicking. The place you are going to situate it needs thinking about , good shelter is a must if you are in a high wind area, mine is dug out in a huge pit with the excess soil forming a bund around it.Drainage is a must as they can get cold and damp in the colder parts of the year. Also they are not pest free , they just move the goal posts and some pests thrive better than outside! I have overhead irrigation which is so easy for watering and cooling it down as they get hot. Mine has a seperate 'dry' room in the back which is my herb garden, I have a chair and table in there! Good luck.