Old building renovation, house built in 1916, multi-family house converted to single-family home, experiences

So the architect estimated 1500€/m2, if you were to have everything done for the 200m2, you now come down to 900€/m2 thanks to your own work?

Not quite. The material costs for the own work are missing. Sanitary equipment, 120 m2 of floorboards, 80 m2 of tiles... and the house is certainly not directly comparable to others. The development of the cold roof must be done, for example, since there is only a ladder so far. Additionally, some items in the estimate are included that are ultimately not necessary. But that was okay for us because we wanted a price range. It then covers possible surprises.

We have a civil engineer in the family who specializes in old buildings. Until a few years ago, one calculated €600/m2 for a simple renovation with own labor and about €1200 for one without own labor at a better standard. But these numbers are no longer reliable; prices have really increased significantly. But this also applies to new construction, so put into perspective. We invested significantly less because we only had to carry out a partial renovation, as, for example, our heating boiler, roof, and facade were still okay. We also did not excavate and seal the sides of the basement. So, major cost drivers were eliminated.

If €1200/m² is no longer current and the price range tends to go upwards (we are aware of that), then I don't think my estimate is that far off. As mentioned, I assume that due to the distance, there is not much more to be done than initially the demolition (depending on what can remain) and then occasionally some auxiliary work here and there. The garden will be managed independently in subsequent years, but it is in very good condition anyway.
When it comes to energy-efficient renovation, what are the main cost drivers? We will do a site inspection with an energy consultant, but I would like to know a bit beforehand. It always makes the discussions a bit easier.
One question, how many replies do I need to post before I can send PMs?

Price drivers can be anything. A rafter insulation costs a lot. A cavity and rafter insulation in [EL] costs significantly less.
Facade is expensive.. I currently estimate 20-30k. Windows in a similar range.

As I said, I would almost say that it is currently hardly possible to calculate. Some prices, e.g. for wood, are said to have already fallen again. Because of Corona, it is now and certainly will be for a long time in some areas simply not clear when there will be something again and in what quantity. There was an article in the Tagesschau today saying that it already starts with washing machines and some bicycle manufacturers still have orders from last year pending, and with many other things it is the same. It is certainly always better to assume the worst case and end up with something left over. But just as well, it could turn out better than expected. Either way, whether building new or renovating, it is currently not a good time. That is my impression at least.

By the way, I believe it is always better if the craftsman can see more precisely what to expect, meaning a shell construction is of course great, or dismantled as far back as it should be. And someone wrote that they are also happy when they don’t have to do that anymore, that was my impression too. Craftsmen can choose their customers and an uncomplicated, already stripped-down shell construction is of course gladly welcomed, I suppose. Also annoying preliminary work, e.g. chasing grooves for the electrical wiring... it also seemed to me that the companies are happy when that was already done.

At the beginning of the year, we had a cost estimate for a roof reroofing with [Aufsparrendämmung], [Biberschwanz], three-sided hip roof, house exterior dimensions roughly 8x6, and a rescue window....39,000€.... Well, that's quite a gulp. It could be a bit cheaper with cheaper tiles, but the professionals charge well.