Thanks for your advice. Makes totally sense for the production process. Not affecting out poduction but anyway - Will go with un-mirrored blocks. 
Here’s a grasshopper script that uses the Elefront plugin to find and replace mirrored blocks. It leaves the original but changed its existing UserText attribute ‘mirrored’ to true.
re_mirrored Rhino Blocks.gh (16.6 KB)
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Another way to tackle it would be to test all blocks for the flipped z, set their ‘mirrored’ attribute to true, gather all true blocks and replace with rotated all at once.
That’s exactly my taste how to do things with grasshopper 
But used my already existing process to do the same magic I used for the quater to produce half of the roof and rotated + copied everything instead of mirroring.
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Hello @interkinactive,
I have been checking your file. I opened the IFC file with Solibri and blocks are correctly imported, did you report this issue to the Revit technical support?
Is there a way to get the transformation matrix of a block? To identify and/or adjust it?
On the revit side it doesn’t use a matrix per say, it uses a flip flag.