Walls is one of the five biggest general contractors in Ireland, along with Sisk, John Paul, Bennett and BAM. So, its performance is a good barometer of the health of the industry and the economy.  In Leaving Cert economics, they tell you GDP is the sum of consumption spending, investment spending, government spending and export spending minus import spending. Investment spending is the most volatile one. When things are looking good, companies invest in new projects. As soon as a slowdown appears on the horizon, they cut investment spending dramatically. Fluctuations in investment spending are what leads to booms and…