sour lagoon
Greetings! 
As a person who has completed the game with all the achievements (but without one blueprint))), I would really like to improve Hello Engineer! If you liked any of my ideas, then use the reactions and comments on this topic! Have fun reading! :)
Inspired by @pearl venture
1. Awards for parts and rocket launch
The launch of a rocket is the end of the creator's mode, which not everyone can get. It seems to me that for launching a rocket we should get an additional achievement, most likely a secret one.
It also seems to me that if the found parts for the rocket are displayed in the menu, some rewards could be added for finding them. For example, plastic, ropes, or even parts for the library, whoo!
2. Nerf attractions
Some of the rides in the creator mode are very funny, and they can be constantly re-run. For example, a Dragon attraction, an Airplane or a Ferris Wheel in a desert location, but some attractions need changes.
For bowling, as for me, we should get more than 15 seconds. This time is enough for dishonest passing, but it will take us at least a minute / 30 seconds to run several cars on pins.
As for the water slide, the situation is controversial here. I don't think anyone can finish this attraction honestly without a bunch of engines. It seems to me that it is worth either increasing the time or moving the platform closer.
3. More materials for creating attractions
What if you need not only plastic, but also ropes to create rides? Or, for example, you can make the prices different. Like, if you can find blueprint/plastic cubes/a hint for opening a club on the attraction. This will make the rides more diverse and give them uniqueness.
4. Changing skins during the game
@pearl venture already had this idea, so I just want to remind. It would be nice to be able to change characters using the menu.