Building a basic longboard

So in another thread people were discussing longboards for cruising around on days you can't be on the water.

Has anyone tried making their own longboard before? I have existing trucks, wheels, and hardware from my skateboarding days, but no deck. I also have some scrap 4' sheets of 1/2" plywood.

Would taking the time to cut out a longboard shape of it, weatherproofing it with say polyurethane or paint and adding some grip take be worth the time spent? I don't plan on doing anything crazy or bombing hills or anything, just something basic to cruise around on from time to time. Would it either have too much or not enough flex? I know some people build their own by laminating several sheets of thinner plywood together and putting it in a mold. I have no interest in building a mold or doing any of that. I'm not looking for anything fancy. I just want to see if it's even worth the time undertaking this as a project.

If it will fail miserably and break or ride like crap then I'd rather just buy a deck and save my time, but if it would work I'd rather make it myself with what I have on hand.