I'm thinking mid June for you depending on how the spring goes.

Given the likelihood of rain, you might want to plan on a tent, just in case.

There is nothing prettier than a wedding in a garden, in my opinion. Perhaps a wedding in a clearing in the woods would come a close second. Tall trees, no underbrush, and an open sunny area. That is nice, too.

I'd suggest asking the folks who run rose shows in your area. It would help if they knew what roses you grow--many once blooming OGRs bloom early, while the Fairy is often among the last to bloom in our garden.

Here is a link that might be useful: Seattle Rose Show

I would plan the wedding around when it won't rain rather than when most of your roses will be blooming. If you're in the Puget Sound area like I am, I would 100% recommend August because that's when we get our dry season. You will also want to check the ENSO seasonal predictions to make sure we aren't expecting an unusually wet summer, although they aren't always terribly accurate.

If most of your roses are hybrid teas or something similar in its blooming style, you can prune your roses in a way that they'll all bloom at about the same time. Take notes on the time between flushes for every rose you have, and then cut off ALL buds (and do whatever other summer pruning you like to make the plants look neat) 1 flush cycle's worth of time before the wedding. I'm sure somebody can describe this process better than I can.

I agree with Zack. Contact your local rose society and talk with them. They will know when the roses will have their best spring flush of blooms. Rose societies usually always host their shows during the height of the local rose season so people will have the best and most blooms to show. For me that's the first 3 weeks of June but you're in a warmer zone and it may well be much earlier for you. But they can also tell you when and how to prune your roses to get them to bloom when you want (well, as close as you can because roses have a mind of their own sometimes) because they often prune to get more and the best roses for their shows. They will also know what kind of roses will do best in your area.

In total agreement with Zack and Seil. The closer the rose people are to your garden, the better the chance for success.

Aiming for a dry period (with bloom) means you won't have to put down a dance floor and rent tents.

I garden on Vashon Island near Tacoma/Seattle. My Roses are USUALLY at their prettiest about the 3rd week in June. Early August can be a real bust. Late August into Sept usually brings another nice flush of them. I would think about adding lily bulbs so if the roses don't make it in time the garden will be glorious with Lilies in June (Asiatics) or July, OT and orientals. And if they both bloom your guests would never forget it!