Maybe do you know, maybe not. I´m one of the the “father” behind Simple 3D Building specification.
I did in my life thousands of 3D models.
Recently is in my opinion the 3D model of Moscow:
definitly teh best 3D OSM model in the world.
My warmest congratulation for that!
By the way: Use also roof:colour and building:colour value for adding of colours for this model.
Best regards!
Marek
Thank you, marek. Kremlin is permanently in progress 
Неужели это сделано веями в ОСМ?
Если да, то, с одной стороны, очень красиво, с другой стороны, похоже на стройку Звезды Смерти из спичек и папиросных коробок. Без клея и ножниц.
I have already “full 3d building specification”. I know, recently are some very important buildings not really “real”. I hope, we can change it. But, what we need is an 3d online modeller which can use this specification. Please wait for this and make not so complicated buildings during this time. Have You seen Washington or London? They have nothing…
It’s still has lot’s of problems, and we all know it. But things are changing.
What do you mean?
Why not?
I mean for example we don’t have spline based 3d surfaces and many others like rotation elements ( donut etc.). We can already do a lot but not everything.