Complex sentence: Such very large, indeed expensive, but "mass produced" homes may sit on large lots: that is to say, an entire division of McMansions may be created (perhaps dozens or more at once), each on a large lot.
Split into simpler sentences: Such very large, indeed expensive, but "mass produced" homes may certainly sit on large lots. That is to say, an entire division of McMansions may be created (perhaps dozens or more at once), each on a large lot.