Providing the project root directory for CMake find_package - c++

Question

When compiling a project on Windows via CMake, which let's say has the Boost library as a dependency, you might do the following:
Run CMake on the project source directory.
It says it can't find Boost, but you can specify ACTUAL_BOOST_ROOT as a CACHE PATH setting,
which will then be picked up and BOOST_ROOT is set, so that FIND_PACKAGE(Boost) can find the
Boost libraries.
I would like to do the same for my own library Straph, but for some reason in my own FindStraph.cmake, I can't pick up the STRAPH_ROOT variable:
# Find Straph library
#
# Once done this will define:
# STRAPH_FOUND - System has Straph
# STRAPH_INCLUDE_DIRS - The Straph include directories
# STRAPH_LIBRARIES - The libraries needed to use Straph
find_path(STRAPH_INCLUDE_DIR straph/straph.h
HINTS
${STRAPH_ROOT}/include
${STRAPH_ROOT}
)
find_library(STRAPH_LIBRARY NAMES straph libstraph
HINTS
${STRAPH_ROOT}/lib
${STRAPH_ROOT}
)
set(STRAPH_LIBRARIES ${STRAPH_LIBRARY})
set(STRAPH_INCLUDE_DIRS ${STRAPH_INCLUDE_DIR})
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(Straph DEFAULT_MSG STRAPH_LIBRARY STRAPH_INCLUDE_DIR)
mark_as_advanced(STRAPH_INCLUDE_DIR STRAPH_LIBRARY)
At least that's the way it seems to me: in my CMakeLists.txt I do something like this then:
SET(ACTUAL_STRAPH_ROOT CACHE PATH "Location of Straph library")
IF(EXISTS ${ACTUAL_STRAPH_ROOT})
SET(STRAPH_ROOT ${ACTUAL_STRAPH_ROOT})
ENDIF()
FIND_PACKAGE(Straph REQUIRED)
INCLUDE_DIRECTORIES(${STRAPH_INCLUDE_DIRS})
But it goes and complains that it can't find the libraries even after I set ACTUAL_STRAPH_ROOT.