Presumably in you original post, when you say wiring buildings, you're talking about lighting. If this is a new layout, and if by modular one can infer that size matters (a bit a least)...then I'd go with DC. This photo recycled from an earlier OGR thread contrasts the size and weight of a 100W AC-output brick vs. a 90W DC-output brick.
DC bricks can be had for about 10 cents per Watt (or less). The 90 Watt DC brick is less than $10 shipped - and has a selector switch to set the DC output voltage. Then, use $1 DC-to-DC converter modules to convert to whatever DC lighting voltage you need. 12V DC for LED lighting strips, 4.5V DC for Menards, Lemax, Miller, and so on.
