Download from the MSYS2 home page http://www.msys2.org the newest MSYS2 64bit installer and run it.
Install it in short path like C:\msys64

Update MSYS2
!!! Open or use the MSYS2 MinGW 64-bit shell
pacman -Syu

If core packages are updated you must close the mingw64 shell forcefully with close button, not just typing exit on it.
pacman -Su

Install Gramps dependencies
Download and install Gramps dependencies
pacman -S mingw-w64-x86_64-python3-bsddb3 mingw-w64-x86_64-gexiv2 mingw-w64-x86_64-ghostscript mingw-w64-x86_64-python3-cairo mingw-w64-x86_64-python3-gobject mingw-w64-x86_64-python3-icu mingw-w64-x86_64-iso-codes mingw-w64-x86_64-hunspell mingw-w64-x86_64-hunspell-en mingw-w64-x86_64-enchant mingw-w64-x86_64-python3-lxml mingw-w64-x86_64-python3-jsonschema mingw-w64-i686-gtkspell3 mingw-w64-i686-geocode-glib mingw-w64-i686-python3-pillow mingw-w64-x86_64-graphviz mingw-w64-x86_64-goocanvas mingw-w64-x86_64-osmgpsmap-git

If you get the following warning No intltool or version < 0.25.0, build_intl is aborting install:
pacman -S intltool

Install Git
pacman -S msys/git

Building and updating MSYS2/MinGW packages
Install build tools
pacman -S --needed --noconfirm base-devel mingw-w64-x86_64-toolchain

We need a place to download and build from source code so we will create folder called "build" inside our home folder
mkdir ~/build

To prevent pacman to upgrade packages we rebuilt for our needs we can assign them to group gramps_fixed and add them to IgnoreGroup list. Open in text editor file etc/pacman.conf (C:\msys64\etc\pacman.conf) and add line IgnoreGroup = gramps_fixed to options section.
[options]
IgnoreGroup = gramps_fixed

In the following area we need some packages other than provided from MSYS2. You can do it in easy way by downloading prebuilt package or hard way by building it yourself.

db
!!! Open or use the MSYS2 MSYS shell
GrampsAIO uses Oracle Berkeley DB version 6.0.30 but MSYS2 have it at version 6.0.19 and most probably never update it to a newer version.
Gramps will ask permission to downgrade database version at import of any family tree created with GrampsAIO bundle. To prevent that build right version of DB.

Easy way
cd ~/build
rm -f mingw-w64-x86_64-db-6.0.30-1-any.pkg.tar.xz
wget https://github.com/bpisoj/MINGW-packages/releases/download/v5.0/mingw-w64-x86_64-db-6.0.30-1-any.pkg.tar.xz
pacman -U mingw-w64-x86_64-db-6.0.30-1-any.pkg.tar.xz

bsddb3
!!! Open or use the MSYS2 MSYS shell
As db version is changed then we have to rebuild Python bindings for Oracle Berkeley DB

Easy way
cd ~/build
wget https://github.com/bpisoj/MINGW-packages/releases/download/v5.0/mingw-w64-x86_64-python3-bsddb3-6.1.0-3.1-any.pkg.tar.xz
pacman -U mingw-w64-x86_64-python3-bsddb3-6.1.0-3.1-any.pkg.tar.xz

gtk3
!!! Open or use the MSYS2 MSYS shell
GTK+ since version 3.20 drag-and-drop code has been rearchitected to move the drag cancel animation and most input handling into GDK, thereby dropping most of the platform-dependent code out of GTK (MSYS2 version of GTK is currently 3.22.10). This change is not yet present in Windows port of code so we have to use older GTK version 3.18 where it still works.
Latest in gtk-3.18 branch is gtk-3.18.9 (previous versions of this branch have working dnd but have other bugs) so we build that.

Easy way
cd ~/build
rm -f mingw-w64-x86_64-gtk3-3.18.9-1-any.pkg.tar.xz
wget https://github.com/bpisoj/MINGW-packages/releases/download/v5.0/mingw-w64-x86_64-gtk3-3.18.9-1-any.pkg.tar.xz
pacman -U mingw-w64-x86_64-gtk3-3.18.9-1-any.pkg.tar.xz

Install Gramps
!!! Open or use the MSYS2 MinGW 64-bit shell
Prepare source
Create directory to store Gramps source in and go to it
mkdir ~/grampsdev
cd ~/grampsdev

Download source
Download Gramps master branch from source repository
git init
git remote add -t master -f origin https://github.com/gramps-project/gramps.git
git fetch --all --tags --prune
git checkout tags/v5.0.0 -b v5.0.0

Setup source
Before using Gramps you must set-it up.
You just use setup build command not install one
python3 setup.py build

Run Gramps
cd ~/grampsdev
python3 Gramps.py -v

It should return something like:
Gramps Settings:
----------------
 python    : 3.5.3
 gramps    : 5.0.0-alpha1-0919763f1
 gtk++     : 3.22.9
 pygobject : 3.22.0
 pango     : 1.40.3
 cairo     : 1.15.4
 pycairo   : 1.1.10
 osmgpsmap : 1.0
 GExiv2    : 0.10
 ICU       : 57.1
 PyICU     : 1.9.3
 o.s.      : win32
Non-python dependencies:
------------------------
 Graphviz  : Graphviz not in system PATH
 Ghostscr. : 9.20

Run Gramps
Keep your GRAMPSHOME separate
echo 'export GRAMPSHOME=~' >> ~/.profile
source ~/.profile
python3 Gramps.py