A 4 foot long straight edge can be used to check your table's flatness.
I used to build .40 sized models in a motel room while on the road...right on a 3 foot long piece of 1 x 12 pine...and the planes ended up straight enough to fly OK.
While you are in the progress of building a plane, you can always use strategically aimed light to sight down and across expanses to see how things look, plus you always have the long straight edge / rulers to use as gauges.
One of the most important views is along the trailing edge of your wing as viewed from the rear. This is where a twist is easily seen before you get too far into the build, or to double check how straight it turned out after you applied the covering.