First of all, thank you for your interest in contributing to the project. Creation of an operating system is a complex process an there are plenty of ways how one can apply own talents and skills.
There is an open channel in gitter where we can gather together, discuss the concepts and make decisions together.
LeOS UI subsystem is under construction and there is a huge area for designers creativity. Feel free to submit an issue with your sketches and artwork.
Your donations are helping to allocate more time for development and attract new people to the project. If funding is the way you would like to contribute, there is a campaign on Patreon with different benefits for the Patrons.