I know nothing

Hi everyone, long time lurker first time posted. I’ve recently purchased a semi detached property (new build). I am on the end of a row - developer has offered me an extra 10m of land marking my overall garden around 20m wide. there is a clause though, the land is strictly agricultural/amenity, and I would need to apply for a change of use to residential. the land will be mine and completely fenced in and part of my garden. Eventually I would like to use the land to house my shed and my office. Question: **Is it worth getting the extra piece, it would be great for the kids , and It’s at a good rate **how realistic is it getting the land use changed ? thank you in advanced