Our construction project - house in Kfw 70 standard

Why do you want to use the sun? To "save" or for ecological reasons?

I think that with the house including the basement it will be tight. 250k is not much. The reserves will probably be used up quickly. Is there a soil survey?

"Outdoor facilities only the necessary: 10,000 €": And when/how will the sensible part come?

You want to prepare a lot, but not do it. With most people I know, it isn't done later either because a) there is no money and they prefer to pay off the loan or b) the wishes/situation have changed.

yes, as preparation for photovoltaics, I also only imagine a conduit from the utility room to the attic, nothing else...

How large should the terrace be and what are you doing about the driveway, parking space, garbage bin area, house podium/entrance, path to the house? So with outdoor facilities, 10k is actually relatively little... we have a property of roughly the same size and spent at least twice as much, and nothing unusual was included... and a fence was not included in the price...

By the way, there is nothing better than a south-facing orientation for photovoltaics etc... except, of course, if there is constant shade there.

When it comes to roofs, it often depends on the operation... for one, a hip roof is inexpensive, for another a shed roof etc. you can basically only compare.