First, to repeat the question: The pasuk says that the Bnei Yisrael brought their donations for the mishkan to Moshe, whereupon the midrash comments ‘peace is great (‘gadol hashalom’.) What has shalom got to do with bringing donations for the mishkan? (see first dvar torah for answer 1). Let’s suggest another answer based on a more accurate definition of shalom… The Rambam (hil. chanuka 4;14) details that the entire torah is to make shalom in the world. How does the fact that we have a mitzvah to kill off amalek fit with that? And we also say in shabbes davening that ‘talmidei chachamim increase shalom in the world,’ yet if one looks at it, talmidei chchamim are the ones who spend the greatest time arguing (about Torah)? The answer here is that
shalom does not mean a mere hippy-ish utopian absence of war and people dancing round a bonfire singing kumbaya. Rather, shalom is from the root ‘shalem,’ meaning complete – and means living up to personal and national potentials in becoming complete. And that’s what Torah does – it makes completeness in the world, and talmidei chachamim increase shalom – ie perfection and completeness – in the world in increasing HaShem’s Presence here, so to speak. Taking this new defintion of shalom into account, this is why the midrash comments ‘gadol hashalom’ at this pasuk, for when we gave our donations for the mishkan and indeed it was built, we reached personal and national spiritual heights of completeness; true shalom (‘shalem’).