Before the National Lottery considers any donations you're going to need a better source of regular funds than a voluntary bucket collection at the side of the road over just 3-4 months.....
You're going to need a financially sound and reputable charity manned by people with a business mindset, a multi-year realistic business plan for what is intended and how to achieve it and pay for it, a contract with the council/BT which defines and controls running rights and legal and safety aspects of charity staff working on the BT track, guarantees from the council that the shed will be rebuilt to modern safety standards.........and more and more...