A while back I needed to make a house for our Sulcata tortoise to get away from the winter weather. After looking through so many options I decided to make one we could use as a bench as well. All in all, it cost me around $100 and a days worth of work, but that was because we went with a good piece of foam and decent fabric, you can keep it under $100 by shopping around or using old material. Since then, it has worked as comfortable seating and a good shelter for the tortoise.
Here is what you need;
After you determine what size you want to go and gather all your supplies, cut your lumber accordingly. Stack up cinder blocks in such a way that you can set the lumber in the slots on the top, like so;
Cut a piece of plywood and foam to matching length, then wrap that piece with the fabric and stretch it tight up top, using a heavy duty stapler on the back side to secure it. Once completed you can add pillows, blanket, back rest, etc.
Now have a seat, and show your sulcata his new home, we added a heating pad too as well as blankets to block the cold out
You can modify this however you see fit, I am only throwing out a sample of what worked for me. I was limited to space but I have seen other friends wrap their whole backyard fence with this type of bench.