The biggest consideration here has little to do with the population but what level of development is your community? A city developmentally similar to 13th century Paris or somewhere in central Africa today might not change much regardless of the height of the individuals. It hardly matters when sleeping on rush mats on the floor and cooking over an open fire while there is hardly any furniture to be concerned with.
If presuming a fairly well developed wealthy/modern community, housing which accommodates both scales of people would be highly inefficient and considerably more expensive - dwellings and private areas would be specialized to be most comfortable for one size or the other. Public areas like restaurants or government offices could be adapted with accessibility in mind, but the added expense is hardly worth it otherwise.
The difference in height between the typical halfling and typical human is considerable - there is very little functional overlap. Think of how well a 3 year old (average height at that age is around 3 feet) functions in a normal house - it simply isn't sized for their comfort. We don't care so much for kids, as they grow quickly and don't seriously do much, but adult halflings need functional furnishings to go about their typical daily lives.
The idea that buildings would all be human sized and often remodeled to fit the needs of different dwellers very much depends on how wealthy your society really is (a significant added expense to the cost of housing would encourage segregation).
Halfling dwellings would be scaled down appropriately, saving massive costs in materials and labor, not to mention significant structural differences to accommodate greatly reduced needs. Building to human standards would constitute gross over-engineering of everything. Even modern levels of wealth would likely find that highly wasteful for half the population.
Cultural differences in design would likely be significant, simply due to different perspectives and functional considerations. Do halflings like a cozy atmosphere of ceilings just above their head, or a reaching distance above like we tend to (which would be rooms only 4 feet high for them compared to the typical 8 foot ceilings where I live), or would they enjoy having what is in effect very high cathedral ceilings in every room? Personally I'm only comfortable with such high ceilings in entry-halls or grand dining-rooms (had I such a thing), but not so much in my bedroom, toilet, or study. These kinds of comfort considerations will determine what kind of housing they will tend to use.
Being half the population, and families being one or the other so it isn't a matter of accommodating an individual with a disability in an otherwise normal household, facilities would be built to suit their particular comfort. I don't see much overlap between species of such great differences in scale on a daily living basis. In terms of working relationships, such diversity would likely be very useful, but probably going home at night to a home built for their own species (after a night out in the pub with their friends of all sorts).