I am trying to change the values of some buildings so that they are tougher, i'm not to fond of the fact that one full bombload from a bomber can obliterate a town.
Certain buildings certainly should be tougher, but a ton or two of properly distributed high explosives or incendiaries will do a pretty good job of obliterating a small town, especially if the buildings are made of light materials such as wood.
Does anyone know the panzervalues that correspond to certain bombs? for example maybe a panzervalue of 0.7 corresponds to a building being destroyed only by a direct hit from a 500lb bomb. Also how many different types of bomb are modelled? does a 1000lb bomb have the same destructive value as a 500kg?
In real life, there's a reasonably simple formula for figuring the blast radius and destructive value of explosives. You plug in a "Relative Explosive Force" (REF) value for the explosive power of a particular type of explosive (TNT has a value of 1, other explosives have a greater or lesser explosive value) and multiply the mass of explosive by a function to determine the number of foot pounds/newtons/ pounds per square inch/whatever of force exerted by the blast at a particular distance. Different materials collapse or suffer damage based on the amount of force exerted against them. For fragile materials, such a glass, people or light wooden buildings, the required force is depressingly small.
My guess is that the formula for blast radius/explosive force has been modeled into the game, but that the REF values have been greatly simplified. So, the bomb type probably doesn't matter so much as the explosive value of that bomb.
I'm also guessing that buildings have some sort of "minimum caliber" of shell/bomb required to affect them, just like ships. Basically, this acts as "damage resistance" - like armor plating, - to determine the minimum force needed to damage the building. Above that level of force, the building takes damage, probably in abstract terms such as "hit points," although it doesn't show until the building is completely destroyed.
I thought it could be possible to change the values and clone certain buildings to make things such as a U-Boat bunker, that may only be destroyed by a direct hit from a 5000lb bomb for example,
I think trial and error is really the only way to go, given the limited amount of info we have and the relatively crude damage model for builldings.
Your "panzer values" will also depend on whether your want destruction of a building to represent complete destruction or functional destruction: a building which is still mostly standing but which has been rendered unsafe/uninhabitable due to bomb damage. In the former case, you'll want to set the panzer values and "hit points" much higher and accept the fact that IL2 doesn't model damaged buildings. In the latter case, you can keep your values lower, and accept the fact that your functionally destroyed buildings look like buildings in Hiroshima after the rubble was cleared.
Finally, realistically, big, tough buildings like sub pens and flak towers, are functionally indestructible by a single conventional WW2-era bomb. Even Tallboy bombs used against sub pens only punched a hole in the roof rather than taking out the whole building. While that might have had a rather dramatic effect on anything inside the sub pen when it the bomb went off, it would have been relatively easy to clear the rubble, scrape the previous occupants off the walls and return the docks to operation - although fixing the "skylight" in the roof would have been a serious engineering challenge.