But connection between random value and my group is red. What the correct way to do something like this? And maybe you can point me to some documentation because I think I didn't grasp some concept pretty well which causes this issue. Inside of building group:
Unfortunately it seems (?) we lost the ability to generate one random value per node tree instance, now all random values are evaluated as fields. Thankfully there is a hacky workaround :
We capture the attribute generated using a random value field on geometry with only one vertex to prevent the overhead of computing the fields on denser geometry, and then we get the mean (or max, or min... doesn't matter since there is only one value to compute) value and use it afterwards.
It can be reduced to a handy node group to be reused later :
I think you have to take a different approach to solve this type of problem.
Instead of generating a shape with random features, then trying to duplicate it. You must generate ALL of your shapes first, then apply the random features to them all.
This example takes a curve, instances some 'floors' along it, then realizes those instances and applies the transformation to the instances, giving you a different pattern on each floor.
I think this class of problem can normally be modified in this way, it just takes a different mindset.