Buddhist temples do have a dress code. Some temples with a lot of tourist visitors, like that of the Emerald Buddha in Thailand, strictly enforce it. They pass out camp shirts and sarongs to all inappropriately dressed comers. Cover the torso from the collarbone down, arms to the (more or less) elbow and legs to the (more or less) knee. No head coverings. Other than that, clean and tidy is good. Many of us carry a lace or sheer jacket or shawl, or a long-sleeved cotton shirt to be worn as a jacket, in the car during warm months.
However, our sect's temples never turn anyone away because of attire. We figure they'll figure it out soon enough. This is both to prevent distractions -- that body builder in his tight tank tops was pretty darned distracting until another gym rat enlightened (pun intended) him -- and also focus our minds on the purpose of our attendance, which is Buddhist practice.