Here you go, I did a quick write up of the build for someone it's got pictures and rough prices (I think you may need to add VAT fro the pipe bits).
The various parts for the pipes I got from my local steel merchants (Devizes steel) so have a look around or google for yours, I found this a much better place for these parts than a DIY store.
I got the barrel for free, just ring around as many garages and friends as you can and you may find one. Mine had engine oil in and was kindly given to me by a local bike garage, I had asked him about a year ago about barrels and he said I can have the barrels if I want but it takes them a long time to go through them so just keep ringing every now and then to check if one's nearly empty.
I think the one you mentioned with a plastic coating is a food barrel and as far as I can tell the lid on those is easily removable with an attached clamp which means you can re-use it as a lid for the smoker, whereas mine had to be cut out.
** EDIT **
Just found out I cannot attach a .pdf file for you. I have uploaded the instructions to here:
https://www.dropbox.com/s/7lndnbdgkom2h ... w%20To.pdfFeel free to download them, I'm not going to win a Pulitzer but it should get you there.