Old rooms are rarely as symmetrical as their photographs. One alcove is wider, one wall leans a little, and an outlet sits exactly where the most elegant shelf wants to end.
Measure the differences before hiding them
Get the openings measured at several heights and depths. Include skirting, cornice, outlets, and any required clearances around a fireplace or heater. The finished design must follow the appliance requirements where those apply; a balanced photograph cannot override them.
Matching lower cabinet heights and a shared finish can create order without making every shelf identical. In an older living room, the right alcove narrowed toward the back and held the owner's record collection; the left needed room for taller art books. Forcing identical shelf divisions would have wasted space on both sides. We matched the lower door line, then let the shelves above do different jobs.
Use the books you own
Lay out books, records, baskets, speakers, and the things you would rather conceal. A tall art book has a more persuasive argument than an evenly spaced shelf grid. Give each side a job, then compare how much display area the room can comfortably carry.
IKEA’s bookcase and shelving range offers examples of open and closed combinations. These are planning references, not dimensions or support specifications for custom joinery.
Review it from the sofa
Print a simple front elevation and look from the usual seating position. On that job, a filler at the outside wall absorbed the crooked plaster, while the visible shelf fronts stayed square and aligned. We checked it from the sofa before making the last trim piece. A few shared lines usually matter more than identical box widths. Choose exact matching when it makes both sides useful.