Hi Casey!
There are many different types of roses that need all sorts of different conditions to grow. Without knowing the types, I can’t help as much as I’d like to. However, I can give you some general information regarding the germination and growing of the seeds. Keep in mind that roses are quite difficult to grow from seed and there will probably be a decent amount of trial and error.
The majority of roses need to go through a process called stratification. To do this, the seeds should be placed in seedling trays with seedling mix. Be sure they are about 1/4″ under the soil. After you do this, seal the whole thing up in a plastic bag so they can set in the fridge for around 10 weeks.
After that is all said and done, germinate like you would any other plant and be sure to have a heating pad underneath. They like a nice, warm environment. After a few weeks, they’ll begin to sprout and once they get to a decent size, it’s time to transplant. While doing this, avoid touching the roots as they are very fragile and it could potentially kill them. Once again, the probability of most of them surviving is very, very low so be patient. The best time to start is when established roses come out of dormancy (typically early spring) so you may want to wait until next year to start this process. I would suggest you try to grow cuttings rather than from seeds for those reasons.
As far as where to place your greenhouse, that will also depend on the type that you are going to grow. If it is already pretty hot, partial shade might be your best bet.
We also have a wonderful few pages on rose gardening that you can check out on our website at: https://www.planetnatural.com/rose-gardening-guru/
Happy gardening!