Is it possible to create the cleanliness layer as a self-performed task?

Whether you can do it yourself is not so easy to answer. In any case, the layer must be within a certain tolerance afterwards. For us, for example, it wouldn't have been worth it in terms of cost/benefit. If you have the exact specification from the architect (e.g. 15 cm 8/16 gravel or similar) of what you need, I would simply ask a sand pit what they charge for the gravel. Then I would ask various civil engineers what they want to charge for producing the layer. If you simply take your specifications from above, for example, you need 10 m³ of gravel (I deliberately took 10m x 10m as the base area). Our civil engineer wants, for example, almost €2 / m² more than the sand pit just for the gravel for "delivering and installing crushed stone / gravel" (so pure material price). In my opinion, it is not worth doing it yourself (ensuring that the tolerances are met).

Mmh yes I have not checked the prices yet. But my basement builder charges about €1500 for this work. That is why my question is which gravel is needed so that I have the possibility to inquire about the prices from the manufacturers.

Hi, as Michael already correctly wrote, you have to create a base layer and have the correct height at the end. It's not just quickly laying down some gravel and compacting it........ And in the end, you probably won't save anything. Not to mention any warranty claims if something doesn't fit in the end. Regards