Is preparing for photovoltaics in new construction sensible?

Always lay empty conduits in a forward-looking manner and at the same time consider what else you might want to route over the roof, e.g. for [later heating radiators] that radiate from the roof overhang onto the terrace.....

Prepare conduit for electricity and network to the parking space in advance as well.

You need two cables per string. Usually, solar cables with 4mm² are sufficient (depending on the length of the cable run). A string has about 18 modules depending on performance. Roughly calculate the roof area, but I hardly know a roof where a 40 or 50 Kabuflex is not sufficient for this ;) Depending on the roof orientation, consider whether both surfaces are suitable for a gable roof and then lay two empty conduits accordingly.

Thank you

I have a gable roof, one half facing Southwest (very good), the other half Northeast (not so good). Would it be worth covering the Northeast roof as well?

That depends on the exact orientation and roof pitch.

thanks

I have a gable roof, 1 half southwest (very good) other half northeast (not so good) would it be worth covering the northeast roof as well?

estimated (not calculated) up to 30° roof pitch worthwhile up to about 1.5K per KWp if there is a high base noise in power consumption (e.g. due to heat pump)
PVSol can calculate that, trial version runs long enough to get familiar with it ...