At the Transfiguration in Mark 9, what did Peter offer to put up?

Answer: Three shelters

Terrified and not knowing what to say, Peter offered three shelters: one for Jesus, one for Moses, one for Elijah.

“Peter said to Jesus, “Rabbi, it is good for us to be here. Let us put up three shelters—one for You, one for Moses, and one for Elijah.” For they were all so terrified that Peter did not know what else to say.”— Mark 9:5-6 (BSB)