Law / Can Builders registered as self employed in Poland and then work in EU? [4]

Can builders register as self employed in Poland? and then work in Europe under an invoice. In other words can they remain registered within the Polish tax system and then do work in Europe-short term contracts 2-4 months? It seems a lot of hassel to get into other countries tax systems for short term contracts. I appreciate some countries make workers work through a local company for payroll tax but not all. Does anybody know the position on this? Also if builders are self employed in Poland do they have a registration number? what is it called?