Typically I've started with a red oxide undercoat. Sure I've decided not to make another red building but it'll make a perfect base for stippling yellow on top of to get that weathered look I'm after.
Early Learning Centre poster paint was used to shade certain areas. This stuff is still soluble when dry so can be a useful technique for adding variation to colours that go on top. It also gives a nice matt, 'soot-like' finish, which is also handy for weathering. As you can see some of the card gaps are still visible but part of me like the look of separate pieces of metal, not one solid cast. I think this would be better justified with some tiny rivets, but as I don't have any I can live with it.
Here's a top view which, to be honest, isn't pretty. The masking tape on the edges isn't great, but then capping them would have been really fiddly too. Ideally a + shaped piece across the top would neaten this all up but I'm still struggling with taking it apart and rebuilding it repeatedly for painting and photographing I can't be bothered with another piece to paint and attach once the thing is complete.
You can clearly see my issue with the sloping lines of the generators profile in the following pic. The extra detail on the vents draws the eye along the same path. But I don't mind it so much now, again I can live with it's imperfections.