engineer report and mortgage

I'm doing a self build and got a mortgage for €120,000 +(€20,000 savings)I thought. Now the engineer who is doing the report for the payments says that my figures are unrealistic and that the bank will not release money when he send in the report. I will be doing alot of the work myself with my brother in law so I think that I can finish it at the most 150ks. the house is 200 sq meters. I'm at a loss what to do. Can I raise the mortgage to €150,000 as the engineer suggested but I fear that I'm tied down with the €120,000. I really don't trust the banks and that is the reason I did not contact them yet.

You don't trust the banks and your engineer don't trust your figures.
200m2 with two persons for €150.000 . How do you insure two persons working on a site for propably 2 years workmanship for this money incl. the material? Imagine one of you lands in the wheel chair for the rest of his life, who would fork out for the entire costs of this accident? It would be the site owner if it comes hard to tough.
Self build is a risky undertakement , working with mortgages and employed people ( strangers working on site) is a complex thing, when you're not willing to take the risk plus labour onto your own shoulder then you should marry your brother in law. Seriously, the project you have in mind isn't easy, though it can be done. Millions of houses are build world wide every year the way you plan to go.
But that is also known in the circles , the mortgage providers have to see where they can make a profit and the engineers, who have an on site look at the matter, will also try to get around a loss.
€ 20.000 savings- is that on top of the site and site developement and foundation and the first batch of material? Or would the €20.000 be designed to pay for that? Is the site (incl. planning permission) obtained, the engeneer paid from that ?
Try the following web page : http://www.iaosb.com/
It's a site of self builders with a lot of considerable information.

Thanks for the reply Heinbloed firstly I have read alot of your posts on other subjects and found them informative. My main weakness in the building process is the paperwork and budgeting. I figured if I spend €150,000 on the house and myself doing the most of the work that it would be sufficent to finish a well insulated solid house. The foundation is down and the slab should be finished next week.The only thing that I did not see coming is if a bank lends you so much money that at a later stage they can say that this figure is not realistic. The engineer said that this is what to expect and I would have more confidence in the engineer than in the bank.