When building a new home, making it ready to install solar in future is cheap, and will save a considerable amount of time and money later when someone does install a solar solution.
Firstly, for either hot water or photovoltaic you should identify a path from the utility panel into the attic near where you would position the solar collectors. Then install a ½ inch conduit along that path through a building cavity, finishing it off above the finished insulation depth so it can be located later. Also, label the conduit at both ends so it can be identified later, and be sure to seal the ends of the cavity around the conduit.
If needed, install an access catwalk in the attic so that the location of the conduit and future site of the solar panels can be accessed easily and perhaps a platform there for the installers to work.
Install 2x8 or larger blocking between roof trusses or rafters directly beneath the future site of the panels, spacing them 24” oc. This blocking should be secure between the trusses or rafters and in contact with the underside of the roof decking to provide mounting points.
For solar hot water you must also:
Identify a path and install two ¾ to 1 inch type L copper pipes from an accessible location in the mechanical room through a building cavity and extending into the designated attic to a point above the finished insulation depth. These pipes should be capped and insulated with ½ inch insulation rated for 250˚ F (e.g. HT Armaflex). All pipe joints should be carefully reamed to reduce flow noise and bubbling, and the cavity air sealed at the top and bottom.
The path in the attic should be as short and straight as possible with space provided in the mechanical room for the addition of a possible storage tank and/or heat exchanger and controls.
Install a four- or six-conductor stranded thermostat control wire along with the pipes. Tape the wire to the outside of the insulated copper pipe and leave a coil of extra wire at each end to simplify later completion/connections.
