I have plywood tele covers, some with metal, some without.. Plywood inner covers, and plywood bottom boards.. Some of the early ones I built warped, so I learned to build them better. Havent had any trouble since..
Some folks say its not worth the effort to make your own stuff.. I think it is, if you have the time.. JUST for the pride of knowing YOU built that hive those bees are living in.. It gives you a sense of pride, and accomplishment.. You will NEVER hear your bees complain about how good your carpentry skill is.
ONE tip about using salvaged wood.. Often, older boards are thicker than 3/4 inch.. if you use those to make your boxes, the tele cover will not fit, so always build your tele covers 1/4 inch wider and 1/4 inch longer than commercial covers.
How I do it..
http://outyard.weebly.com/bee-hive.html I will be updating a LOT now that its getting COLD outside! Keep checking back!