Builder's Hut at Town Hall 18: 5 of them, max level 8. Max level per Town Hall, with how many you can build in brackets: TH3 1 (5), TH4 1 (5), TH5 1 (5), TH6 1 (5), TH7 1 (5), TH8 1 (5), TH9 1 (5), TH10 1 (5), TH11 1 (5), TH12 1 (5), TH13 1 (5), TH14 4 (5), TH15 5 (5), TH16 6 (5), TH17 7 (5), TH18 8 (5).
Tap a Town Hall to open this item there. Dashed: not available at that Town Hall yet.