Build Buy needs to include door and window designs for all room heights for every width. There are tons of doors and windows that I never use because a) They don't match anything else; b) They only come in one wall height; c) They don't have options for single, double, triple square widths. Also - windows should be able to align with each other. Spending hours designing a house that has a unified look then realizing one of the windows 'snaps' in place out of alignment - throwing off the entire design.
All foundation and stage textures MUST have a matching wall cover - same issue, can't use many of the foundations designs because they don't match anything - and the stairs don't match either.
Color swatches need to match across all packs. Really sucks when you have a design where everything goes together but that end table is just the wrong shade and it makes the whole design look stupid. Better yet, bring back the color options from previous Sim games where you could make and entire room set with the same wood grain, matching fabrics, metal finishes, and color coordinated features.
Curtains need to stop taking up so much space (blocking doors, can't have tables against them, etc.) - and like the windows, they need to come in all three wall heights and be available for all window widths. They have the same color swatch problem, so again the color palette controls from previous Sims games would help here too.