Commentary for Numbers 23:29

ויאמר בלעם אל בלק בנה לי בזה, “Bileam said to Balak: ‘build for me in this spot, etc.’” On the previous occasion the Torah reports Balak personally as building the altar (verse 14). Perhaps the reason was that at that time Balak still entertained some hope that Bileam would get around to cursing the people. Now, after Bileam had blessed the Israelites twice, he considered the situation as beyond repair and he was in no hurry to build more altars but took his time before following Bileam’s instructions.