With regards to trellis’ this is the most common question that I generally get. Depending on who you ask, you’ll likely 50% of people on one side of the trellis saying that you don't need to build your trellis the first year and 50% of people on the other side of the trellis saying you should build your trellis the first year.
My answer to the question:
If you are new to planting grape vines, it is ok to just plant them and just run them up a stake for the first year. If you are planting a huge vineyard, I would recommend getting the trellis up as soon as possible.
The reason why I say it is ok to keep the trellis off for the first year for new grape growers is that a lot of new growers have challenges with keeping weeds off the first year due to lack of equipment. Having a trellis around the vines can be a challenge to keeping the weeds down. This really should be a priority the first year, as it is very important to keep the vine free of mildew and healthy.
I live in a climate with lots of rain fall and the grass is always green even in the summer. It seems like every new grower spends a tremendous amount of time wiper snipping the weeds around the vines. Most commercial growers have some sort of grape hoe or automated mechanism for tilling around the grape vines. If all you have your first year is a till behind your tractor then by all means keep that trellis off the first year. This way you can skim off the weeds around the vine and keep them as clean as possible.