sewing related advice please?

[wicker-girl.livejournal.com]

There's this amazingly cool coat I saw that I want, it's tweed style material but flourescent red green and pink tartan (sounds abysmal but somehow *works*) and double breasted with these big chunky buttons, BUT it's about 3 sizes too big (it's HUGE) and really boxy, it makes eveyone look like a big rectangle like a toy robot. But I want iiiit... it's £25. Hmm. Should I get it and try and alter it to a smaller size and more flattering shape, or shall I give it up as a lost cause? I don't have that much experience making or altering clothes, but I do have a sewing machine at home, and my granny might help me if I asked her nicely. I guess I've got a while to decide, it's been in the shop for ages cause everyone loves it and wants it but finds it's too big and a weird shape so doesnt buy it. Your thoughts please?