Recursive makefile for c++ source - c++

Question

I've been struggling with makefiles for a while now, since I don't really get how they work...
My directory structure is as followed:
--bin/
--build/
--includes/
--src/
----classes/
------somefiles.hpp
------somefiles.cpp
----states/
------somestates.hpp
----main.cpp
----few-other-files.cpp
--Makefile
--.gitignore
Which worked fine with my makefile, until I started adding those subdirs, classes and states
I can't seem to find how to include those subdirs in my makefile which is:
CC := g++
SRCDIR := src
BUILDDIR := build
TARGET := bin/game
SRCEXT := cpp
SOURCES := $(shell find $(SRCDIR) -type f -name *.$(SRCEXT))
OBJECTS := $(patsubst $(SRCDIR)/%,$(BUILDDIR)/%,$(SOURCES:.$(SRCEXT)=.o))
CFLAGS := -g -Wall
LIB := -lsfml-audio -lsfml-graphics -lsfml-network -lsfml-system -lsfml-window
INC := -I includes -I /usr/local/include -L /usr/local/lib
$(TARGET): $(OBJECTS)
#echo "Linking..."
#echo "$(CC) $^ -o $(TARGET) $(LIB)"; $(CC) $^ -o $(TARGET) $(LIB)
$(BUILDDIR)/%.o: $(SRCDIR)/%.$(SRCEXT)
#mkdir -p $(BUILDDIR)
#echo "$(CC) $(CFLAGS) $(INC) -c -o $# $<"; $(CC) $(CFLAGS) $(INC) -c -o $# $<
clean:
#echo "Cleaning..."
#echo "$(RM) -r $(BUILDDIR) $(TARGET)"; $(RM) -r $(BUILDDIR) $(TARGET)
.PHONY: clean
Problem: Fatal error: can't create build/classes/stateManager.o: No such file or directory
Normally, the problem is that it can't build the directory. But I thought the mkdir -p would solve that.
Any help is greatly appreciated.

Answer 1

Replace:
mkdir -p $(BUILDDIR)
with
mkdir -p $(#:D)
Another way is to let make treat directories as targets and have them automatically created for you, so that you do not have to clutter your recipes with mkdir -p invocations:
.SECONDEXPANSION:
# Make the object file depend on its directory using order-only dependency.
$(BUILDDIR)/%.o: $(SRCDIR)/%.$(SRCEXT) | $$(dir $$#)
$(CC) $(CFLAGS) $(INC) -c -o $# $<
# Let make create the directories for your targets.
%/:
mkdir -p $#
# Do not remove the directories because they are "intermediate" targets.
.PRECIOUS : %/