working on small LAN for a office, going to use windows server 2012 with AD which ip range is suitable for this. there's like 13pc's & 1 server
As Ron Maupin already mentioned, anything in those three ranges defined in RFC1918 will be fine, those are assigned for local networks.
Personally, I wouldn't pick one of the more obvious ranges like
10.0.0.0/24 if you ever plan to offer services like VPN for remote workers. Most of the home routers use those by default for their local networks, so it can be wise to stay clear of ranges to prevent an overlap.
I'd pick a range from the
172.16.0.0/12 network (which seems to be less used in home routers), and not the first
/24, so for example