How is a 400k loan financible without equity? Net equity at €4,500

I don't understand the connection? Our plot cost €60,000. Does that mean we are only allowed to build a €150,000 house on it?

Here is a conversation from practice:
Seller: The plot costs €50,000.
Prospective buyer: Oh, unfortunately, that's too little for us. Our house costs €400,000, so we need a more expensive plot. Is €120,000 also okay?

Now we're drifting a bit

The judgment of the masses sounds devastating, but you are honest and warn us. This is exactly the feedback I needed. I will answer a few more questions, maybe that will change something.

he: permanent employment since the beginning of the year. Net equity 2300 plus holiday pay plus 13th salary. Equity increases every two years. up to 5000 gross. Then it's over for now. 32 years old

she: tenured civil servant for life from October. Net equity 2200 (health insurance already deducted) rises continuously. Family allowance etc. 27 years old

so far we have her 10K equity, me 20K equity. Everyone saves at least 500€ monthly. In two years the loan will start running. That means we will save a total of 24K more. This total of about 50K is for floors, painting work, exterior work, unforeseen costs, etc.

of course we could also put in 10,000 or 20,000 as equity, but that is nothing the bank told us. So we prefer to keep it as a safety cushion.

The foundation slab is already included in the price.

20% of a 400,000 loan would be 80,000. And by then I’m 38? How am I supposed to pay that off by retirement? That doesn’t work