I sometimes put stuff on an account for someone at travis perkins, they get robbed blind, never any discount.
I've worked for a few firms who have accounts with Travis - but when dealing with big outfits like Travis you have to have a trade credit account, volume and have negotiated discounts for the categories of materials you are buying (e.g. timber. sheet materials, screws, plumbing supplies, etc). The discounts you can get out of these big guys are sometimes really amazing - providing you have the volume (e.g. full packs of timber or PB, etc) and a properly set-up account.....
Last firm I worked for we split timber purchases between a small local timber yard, a major builders merchants and a national sheet materials supplier. The small guys were slightly better on price and could resaw in-house if needs be, but their delivery wasn't always reliable (and TBH who wants to be unloading a wagon at 4pm on a Friday afternoon on their jack in the dark and rain?) and quality was an issue at times. The bigger guys were often better on delivery (i.e. 2 days means 2 days, just don't expect anything tomorrow unless you collect it yourself), their prices on sheet goods were often far more competitive and they delivered exactly when they said they would. I still think that we ran three accounts to get more credit, though.
And as for screws, fastenings, sealants, etc - never, ever buy them from a builders merchants because they are always cheaper from a specialist ironmongery or fastenings firm if you are buying sufficient volume to get an account (a self-build might be sufficient for that)