So I am a gui designer, I worked with them for almost a year and I made a simple simulator gui to test my skills and maybe make some money. So here are the gui:
I am for hire.
roblox name: so_er
Discord name: So_er#1744
Looks good, I cant wait to play a sim with these in it, the inventory bar could be made a little longer though?
These are very good interfaces, I wish you luck with your simulator. 
In my opinion, the color scheme isn’t too great. The inner frames for the yellow bar with 000 is way too dark, and the text almost blends in with it. The same goes for the pink bar.
For the rest, there is just too much of the same color. A bit of variety would be nice.
Speaking of which, all the frames look too similar. There’s not enough detail in them. For example, the inventory UI has no storage and equipped display (if applicable). How will you let the player know how much storage he has left?
Moreover, the robux shop does not look special and eye-catching, it’s a dull green color. Generally, you want robux shops to be attractive and brightly colored. Or it could have a different, unique design so that it’s differentiated from the other UI, showing a importance to that UI. Visual impressions play a part when players decide if they should buy something or not (of course though, what the product actually gives plays a major role).
Overall, not too bad, you just have to change the color scheme up a bit to make it look more colorful which is what you want to go for in a simulator. You also have to think about UX (user experience) (e.g. the currency bars being too hard to read, the inventory UI missing key details such as storage space, etc)
Looks Nice!
The only change I would suggest is the Yellow part of the UI.
Instead of just lowering the color for shading, try making the yellow warmer or cooler.
Pretty good but, where is the price if anyone wanted to hire you?
2-6k robux and the guis hmm like 2k I dont really know.
