Most UV protected greenhouse polyethylene comes with a 4 year guarantee. Most non UV protected (construction grade) material has no guarantee and lasts from 3 mo. to one year.

Get the greenhouse poly. The cheap stuff is a waste of money.

Use Greenhouse poly like this. If using on PVC pipe use felt tape so the PVC doesn't react to your poly and void your warranty. Usually the plastic will last 4-5 years with direct contact but use paint or felt tape to make it last longer. Fasten the poly with ABS snap clamps.

Forget the rolled poly stuff...it simply won't last and you'll not be happy with an improvised 'fit'. I used a 6x8' ShelterLogic for 6 or 7 years, replaced just last winter for a 10x10x8' high unit by the same folks. (I think it was just $150 or so "on sale" at Northern Tool.) This is my 'temporary' GH, intended just to keep the frost off hardier plants for which there isn't enough room in the stick-built, 10x16' main GH. Shelter Logic has a wide range of products - up to circus tent size. The units are well-engineered and the fabric will last, well, until you outgrow it.... The earlier one sloughed off a 17" snowfall the first year, unlikely with a home-engineered and -built unit.

There is also a reinforced polyfilm available that has a rip stop cord in it. This will help to increase the lifetime expectancy of the film.