What size should i make the uis when i am making it?

I normally use 150x150px

Can some recommend me some size in photoshop?

I am a bit confused by what you are looking for. If you are talking about creating textures for user interfaces, Roblox accepts up to 1024px by 1024px . If the UI’s size for the given texture becomes more than 150x150, it will appear much more blurry compared to 1024x1024.

Depend the UI’s is for, best way to find out is first, figuring out platformes average sizes, eventually the Max & Minimum, so let’s say iPhone 5 & Full HD

Then, you can go ahead and simulate the size & Calculate the necessary canvas with Placeholder Frames : (ex : 1036x69 to fill it perfectly (unless unproper scalling)

I recommend a larger size within photoshop than 150x150 because the roblox screen is pretty big, once you expand the size of a UI, the quality diminishes. In graphic arts, we create UIs at a large scale so that the pixel ratio within the image stays at quality levels when sizing down. You should not need to size up, that will just make pixels become blurry and fuzzy, start at sizes like 1000x1000+.