help please on building my own cloche thingy?

Not sure when a cloche becomes a small polytunnel! anyways I have been reading about building a tunnel thing from blue water pipe. I have looked at mu local screwfix and they do a 50m roll for £24 something. Is this about the price you all pay? so from looking at the instructions there are a few ways but i think i will go with the dowelling hammered into the ground then sliding the tubing over. Does this sound about right? Thing is I am a bit confused on a) what to cover it with and b) what to use it for! Do I make one the length of the plot and uncover it to weed or feed or whatever I am doing?

I have some debris netting which i salvaged from a tip I could use or I have some fleece.

I presume its to protect from cold and birds and things which there are millions on my plot as its by a nature reserve. I think I can use it on the strawberries when they get going. Last year I tried some chard but that got ravaged by something but I dont know what so could I use it for this?

sorry for the questions but I am a real starter here! And am guessing it wont be used until the plants have started to grow or do i use it before i plant to warm it up a bit.