Tag $$SYSR$

Shows total and free space for any device on Android
$$SYSR:path$ sets path for current context
$$SYSRxyformat$ shows total and free space on device for current context

x : F for free space, T for total space
y :
B shows result in bytes;
K in kilobytes;
M in kilobytes;
G in gigabytes;
T in terabytes
P in petabytes
<null> : prefix will be calculated automaticaly
format : format string for float value:

%f 123.456001
%.1f 123.5
%1.5f 123.45600
%10f 123.456001

For more info about formatter see Android Developer Reference

Open terminal and run df
$ df
Filesystem Size Used Free Blksize
/dev 311M 44K 311M 4096
/mnt/asec 311M 0K 311M 4096
/mnt/obb 311M 0K 311M 4096
/system 590M 513M 77M 4096
/data 12G 3G 8G 4096
/cache 1G 32M 1G 4096
/system/vendor 4M 4M 864K 4096
/mnt/sdcard 12G 3G 8G 4096 <-- on old phones this is external sdcard
/mnt/cifs/video.general 1863G 1728G 134G 4096 <-- if you use external shares, you can add it to widget
/mnt/external_sd 1G 32K 1G 32768 <-- if you need external sdcard

Now change text in widget config to:
@@FDIGI000@RAM FREE: @@#0088FF@$$SYMF$B
@@#00FF00@STORAGE:@@#0088FF@ $$SYSR:/data$$$SYSRF%.02f$ /$$SYSRT%.02f$
@@#00FF00@SDCARD:@@#0088FF@ $$SYSR:/mnt/external_sd$$$SYSRF%.02f$ /$$SYSRT%.02f$
@@#00FF00@VIDEO:@@#0088FF@ $$SYSR:/mnt/cifs/video.general$$$SYSRF%.02f$ /$$SYSRT%.02f$