hookooekoo
Senior Retro Guru
You can get away with a few mm difference. If the spokes are slightly too short, it may still work, but there could be a small amount of spoke thread visible on the finished wheels. In the opposite case, the risk is that you run out of thread. Those who are perfectionists might not like having a little spoke thread showing.
Also bear in mind that if the wheelbuilder doesn't have the exact length required, they may use a spoke that works, but results in wheels where a little spoke thread is showing. This is one reason why I now like to build my own wheels. If it goes pear-shaped, I've only got myself to blame for how it looks.
Another reason is that last time I got someone to build some wheels for me, they said they didn't like working with lightweight rims (this was a road bike wheel build). When I got the wheels home, I had to spend several hours finishing the trueing process, as it seems that lightweight rims are time consuming to get perfectly true, and they stopped trueing the wheels when the money ran out. For me, that was the end of paying other people, because I had basically paid someone the whole wheelbuilding fee to supply spokes at the correct length, lace the wheels, and then I had to finish the hardest part of the job myself. Next time I did the whole job myself, took my time calculating spoke lengths, and it came out perfect.
Also bear in mind that if the wheelbuilder doesn't have the exact length required, they may use a spoke that works, but results in wheels where a little spoke thread is showing. This is one reason why I now like to build my own wheels. If it goes pear-shaped, I've only got myself to blame for how it looks.
Another reason is that last time I got someone to build some wheels for me, they said they didn't like working with lightweight rims (this was a road bike wheel build). When I got the wheels home, I had to spend several hours finishing the trueing process, as it seems that lightweight rims are time consuming to get perfectly true, and they stopped trueing the wheels when the money ran out. For me, that was the end of paying other people, because I had basically paid someone the whole wheelbuilding fee to supply spokes at the correct length, lace the wheels, and then I had to finish the hardest part of the job myself. Next time I did the whole job myself, took my time calculating spoke lengths, and it came out perfect.