Grammar of Modern Greek language: http://pi-schools.sch.gr/gymnasio/gr..._c/s_1_200.pdf
Syntax of Modern Greek language: http://4dim-ampel.thess.sch.gr/ict/S..._ellinikis.pdf
Right click and "save as" to download the files.
These are the exact same books that students in Greece are given and study in schools. The books are in Greek but they are good reference for any issue, and you can ask for any clarification or explanation here.