TL;DR: I'm a competent and careful handyman who cares deeply about the quality of my work. I'd like to present the idea of doing repairs and minor renovations to my rental for only the cost of materials but I don't want to be offputting to my landlords about it.
Background
I am fairly handy and enjoy building things. I'm finding myself immensely enjoying woodworking and construction, and have spent a lot of time reading about techniques, best practices, etc. I consider myself to at least be competent at this point. I'd like to continue to increase my handyman skills.
I live in a house which I rent directly from a couple who owns it. I love the area, the yardspace provided, and the house has a tremendous amount of potential. I haven't been here long but we are on good terms and I always pay rent before the due date. With their permission I've put up some non-permanent structures (chicken coop, fence, gardens) and I'm proud of my work.
Current Situation
The steps to the back yard are starting to seriously fall apart and were clearly put together by someone with little knowledge or who didn't care to do a good job (tons of nails in random places, uneven cuts, random shims, things don't line up, etc). I'd feel confident I'd be able to remove them and instead build something which would look nice and last much longer.
There are many other things I'd change about the house if I were able. The cabinets are abhorrent. The bathroom linoleum looks like it was laid by a child and could only be described as garish. The baseboard is uneven and patchworked in many rooms, and non-existent in some places. Etc.
Proposal
Here's what I'd like to propose. They plan on moving into this house in 8-10 years. I'd like to rebuild the steps as a sort of "test run" project and hopefully make them feel comfortable with me eventually doing more work. They'd take the cost of materials out of my rent (I can provide itemized receipts). I'd work for free, get to learn more skills, and I enjoy the work. In exchange they'd be moving into a nicer house for much cheaper than it'd have cost a professional to do the work.
I think this arrangement sounds very reasonable. I'd love to do the work but I don't want to pay for materials I can't take with me upon moveout. They can even look at the non-permanent projects I've done to showcase that I'm not a sloppy worker and would do a nice job.
Worries
I am only asking because I worry that if they say no, it will set a precedent for me never being able to do any sort of project with the house. Furthermore if they say no and send someone to work on it instead it'd be a huge hassle for me to have people working on the house while I'm occupying it and there's no guarantee they'll do a nicer job than whoever built the stairs initially.
I understand why many landlords are apprehensive about this sort of thing since many tenants don't do their research and would likely do a poor/sloppy job. How can I present this and convince them that I'm not that kind of person and want to create something I'd be proud of?
Notes
[I] Volunteered [to build the chicken coop and fence and other projects]. I wouldn't expect them to pay for my personal projects, just for the actual improvements to the house proper. I don't mind paying with my own money for the garden and other yard projects since I may take the raw materials with me upon moveout (unless they really want them and I'd probably sell them for a small fraction of what it cost me to build)