"Έχουμε σχέδια του πύργου μας."
Μετάφραση:We have plans of our tower.
Normally in English plan is followed by the word for. We have plans for our tower means we have a project for our tower, I have plans for the summer etc. If you say we have a plan, in the singular, of our tower it means you have an architectural drawing of the tower. If the sentence has the first meaning it should be for and if the second a singular noun would be correct.