Example Over Winter /Quarantine Tank

2"x12" planks, 4'x8'x3'deep, Epdm liner, Ultima 2000 mechanical filter/bioconverter, blue barrel contains 2 lines of SpringFlow biomedia (380sqft), 57 watt Aqua Ultraviolet UV at sterilizing flow rate, Note the PVC conduit w/leaf mesh lid which is open against the wall. Corners are joined with 4" lag bolts from 4' end piece to the 8' span, as well as from both directions into a 4x4 internal to the structure. (OVERKILL IS GOOD IN MY BOOK!!) You can also see the platform on which it sits to keep it of the cold floor.
For a smaller filter foot print a great choice is the Nexus EasyPod. Mechanical and much higher surface area kaldnes biomedia in less space than the blue barrel. The pictured system was constructed before we carried Nexus and for nearly the same cost.

Other options include show tanks and medium sized inflatable pools that you can find at places like Toys R Us. They require less construction and are temporary, but don't use the space as well since they are round.