General builders merchants are just known as almacenes de materiales de construccion. They usually sell cements, bricks, blocks, sand, gravel, vigas, rasillones, bovedillas etc plus sometimes drainage products, building chemicals, insulation, tiles etc plus sometimes bathrooms, taps etc.
Then you have almacenes de maderas for timber.
Carpinterias (de madera/aluminio) for doors and windows.
Ferreterias for tools, ironmongery, safety gear, sometimes other building products such as drainage, fencing, building chemicals, cable etc.
Ebanisterias for cabinet making (kitchens etc).
Fontanerias for plumbing and drainage, water heaters, sanitary suites etc.
Carpinterias metalicas or forjas for rejas, gates etc.
Almacenes de hierros for reinforcing bar, steel beams etc.
You also have almacenes de pinturas for paints, varnishes etc.
Suministros electricos for electrical supplies…
plus many variations on a theme…
And not forgetting bricolajes (eg Leroy Merlin, AKI, BricoMart, BricoDepot etc) which are B&Q-like DIY type stores.
You will find that the builders merchants in your area will stock a mixture of some or all of the above. Trades are a bit more “separate” here than in the UK. Sometimes you have to do a great deal of shopping around to find stockists of eg plasterboard.
I’ve had no trouble “opening accounts” though it’s very informal round here (give your name and address…pay at end of month!). Cash still the preferred means of payment… 😉