In short: what to decide before tiles
Before choosing bathroom tiles, six things need deciding: who uses the room and how, where the toilet, basin and shower go, which models of sanitaryware and taps you are fitting, what goes inside the walls (frames, valve bodies, drains, extraction), where light and sockets are needed and how the surfaces will be looked after. Tiles come last, because the tile layout depends on all of the above.
Start with the tiles and you end up fitting the sanitaryware around them, with the compromises landing exactly where you see them every day.
Who uses the bathroom and how
A couple getting ready for work at the same time needs two basins and perhaps a separate WC. A guest bathroom manages with a compact basin and a shower. With young children, a bath is more practical than a shower for the first years. If elderly parents visit, think about a level-access shower, grab rails and room for a seat; our article on accessible bathrooms covers this in detail.
List the morning and evening routines and the priorities: shower or bath, surface space by the basin, closed storage. Mark how doors and units open and check the circulation. A second basin added purely for symmetry, with no elbow room between the two, gets in the way more than it helps.
Layout and sanitaryware models
The toilet position is set by the soil stack; the shower position by whether a fall to the drain can be achieved. The layout is built from that. How to squeeze space out of a small bathroom is covered in a separate article; here the order of decisions matters more.
After the layout come the models, because they determine what is hidden in the wall. A wall-hung toilet needs a frame. A concealed shower valve needs a body from a specific manufacturer, fitted before tiling. A ceiling-mounted rain shower needs an outlet in the ceiling and enough height. Changing the model after the body is installed usually means replacing the body too and opening up the tiles around it.
Concealed systems: water, air and electrics
Drainage, waterproofing and ventilation are coordinated by the responsible professionals based on the systems chosen. A catalogue picture does not prove it can be done in your home: a level-access drain needs enough depth in the floor slab, and extraction needs a duct to the outside.
Electrics near water have their own rules. Spain's low-voltage electrical regulations define zones around baths and showers in which the type of equipment and its protection rating are restricted. So mirror lighting, a socket by the basin, a demisting mirror or an electric towel rail are planned with the electrician according to those zones, before plastering, not improvised after tiling.
Upkeep: think about Barcelona water
Water in and around Barcelona is hard, and limescale builds up quickly. Matt black taps and dark tiles show it most. Glass with an anti-limescale coating is noticeably easier to clean than standard glass. Cement grout in a shower darkens and needs care; epoxy grout lasts longer, but laying with it costs more.
Natural stone is porous: it is sealed and cleaned with the products the supplier recommends. A "stone look" does not define the material: marble-effect porcelain and real marble are maintained differently. Read the manufacturer's care advice for each finish and compare samples before ordering.
The tile layout follows the sanitaryware
With everything above decided, the tile setting-out is drawn. On the drawing, joints are lined up with the centre lines of the toilet, basin and taps, niches are sized to the tile to avoid thin cuts, and the starting line is chosen so that full tiles sit where the eye falls most.
This is where it becomes clear which format suits. Large slabs mean fewer joints, but in a small bathroom with many outlets they turn into a patchwork of cuts. A mid-size format sometimes lays out more cleanly. You cannot see that without a setting-out drawing, and on the wall it is too late.
One list, and two bathrooms
Put sanitaryware, taps, vanity, mirrors, lighting, accessories and tiles into one list with references and statuses. Flag anything undecided and confirm compatibility before buying: a valve body from one manufacturer and a trim from another will not fit together.
If there are two bathrooms, as in the 109.80 m² Urgel flat in the Eixample, it helps to give each a role and work out its own scenarios rather than copying one design twice. We agree the selection and scope for your bathroom after visiting and studying the room.