Well, with 200,000 it’s already tight for the house. We built 11x10, but with 2 full floors and paid 290,000. That was before the extreme construction boom and even now everything isn’t finished yet.
100m² footprint and the attic converted – with this budget I would seriously reconsider if you really need that many rooms. Better smaller and forget the office/guest room – that way it’s affordable.
200,000€ is already the (fixed) offer for the house, of course it will get more expensive for things like some electrical work etc., I already factored in a 10,000€ buffer for that. Things like flooring, painting, fireplace, better bathroom etc. are anyway excluded from that price. Otherwise, I don’t see what would significantly increase the price. We already have great additional features included in the price (aluminum shutters, lift-and-slide door etc.), you can hardly get more.
The problem with a smaller house is not the missing guest room on the ground floor, but that also upstairs one room (or dressing room or storage room) disappears. At some point it’s a problem storing stuff without a cellar (be it just office stuff, but also vacuum cleaners etc.). Having 10 m² more garden area doesn’t justify the lack of space inside the house, in my opinion.