Green’s Dictionary of Slang

build v.

1. [late 19C+] (orig. Aus.) to prepare, of food, drink, a marijuana cigarette etc.

2. [1930s] (US Und.) to create confidence or apparent friendship, for the sake of enticing a victim; thus built up adj.

SE in slang uses

In phrases

build pigpens (v.) [the practice of woodcutters who pile the wood on their carts in the shape of a pigpen; thus making the pile, which is hollow, appear larger than it is]

[1950s] (US) to deceive, esp. for a merchant to cheat a customer.