Making a DIY Courier / Messenger bag

For those of you without the resources/money/access to tarp and water-proof materials for bag making, what about buying a couple of IKEA bags, £1 each and big enough to cut up and get enough material for the lining/outer of a large messenger bag. It could work maybe? Even if the material was doubled up for extra piece of mind. I've been using IKEA bags for heavy items and laundry and in two years I've not had any of the bags degrade or break. Even the handles could be recycled as they are surprisingly strong.

IKEA's started doing smaller versions of the big blue bags now, so possible pannier bag liners?

I don't make bags, so if the suggestion is cack, sorry!

Can I bump this post to this thread?

I've started to use the large bag to line my sports holdall, it works a treat especially for containing my sweaty gi and keeping everything else in the bag dry and smell-free but also as the holdall isn't waterproof, it keeps a clean gi dry (the weather has been horrendous lately). I haven't made my bag from scratch but I'm certainly trying to improve on it to fit what I need them for. My next stop is to stitch a zip onto the Iiner and secure the liner into the bag permanently.