I know people love to save money, but by the time you paid for a cheap door with no guarantee, paid for all the tools/materials required to fit the door, installed it, paid for LABC to sign it off, the general stress of everything involved, you might as well pay a few hundred more and get a local company in, youll get a decent job done, guaranteed for 10yrs, signed off fensa/Certass, insurance backed guarantee, no further worries as they'll come back rectify if there are issues during the 10yrs.
We've just helped a customer out, the builder has walked off site due to the customer being too involved, customer had bought all the materials, windows, doors, tiles etc themselves, everything cheap and most things not fit for purpose. The doors we installed for them were wrong size, wrong spec, rooflights were wrong spec, they've now ordered everything again at the size/spec it should be.
They thought by buying everything themselves instead of the builder they'd save..... Far from it
Do it right the first time