Hi - in Vol 17 of Fine Woodworking, there is an excellent article about timber framing by Ed Levin in which there is an illustration of a cart like you referred to. I have made two of the these carts. There is nothing complex about them. You merely make a square box of a width suitable for your project - I used 2x4sx18" - to hold an axle of sufficient strength to carry your heaviest beams. Then you have to use wheels that will also support this weight. My heavier cart used a 1" steel axle with heavy duty wheelbarrow wheels. I was able to easily move 9"x11"x 18' railroad switch-timber weighing over 800 lbs by myself with this cart. I would recommend that you keep the wheel height and consequently, the box height to a minimum as this means you you can more easily load your beams onto your cart, especially if you're working alone as I was. Another valuable aid in moving big beams on a hard, even surface is 2" PVC pipe used as rollers. Good luck with your project, jekbear