I'm rebuilding a rear wheel for a Trek 1000 I'll probably sell, and I've wound up with a mix of 1.8mm and 2.0mm straight gauge spokes. The original spokes were 1.8mm black, and I bought 14 new black spokes to replace a hodgepodge of 2.0mm silver SS and UCP earlier replacements - it'd be harder to sell as it was. However, after I'd laced up the new spokes I found that the LBS had mistakenly sold me 2.0mm spokes instead of the 1.8mm. One of the originals broke when I detensioned it, so I bought another couple of 2.0mm spokes.

Now that I basically have half 1.8mm and half 2.0mm spokes, what would be the best way to lace the wheel with them? I don't want to spend any more on the bike - I probably won't get my money back it as it is. The lengths are 290mm DS and 292mm NDS, so I can probably use them on either side. I'm probably stuck with 3x lacing, but that's not a bad thing. I figure I can:

1. Lace the DS with 2.0mm and the NDS with 1.8mm.
2. Lace all trailing spokes with 2.0mm and the leading spokes with 1.8mm
3. Randomly intermix the spokes

Which would be the best? Any recommendations? Bad idea?

DS 2.0, NDS 1.8, may even work better because both sides will be experiencing more similar amounts of spoke elongation. Also I would really be annoyed building a wheel with dissimilar spokes on the same side because it makes comparing tension harder.

The NDS is going to typically require a spoke "about" 1.5mm longer (give or take depending on CTF dimensions of the hub.)
I build most my wheels with thinner NDS spokes than DS. I wouldn't consider the reverse.

I agree.

+2. Hopefully you have nipples that are proper for each spoke gauge but use the same wrench size.