Floor One, First Story, Ground Floor
Noun
いっかい
ヘビたちは一階でかっているんですか？
Do you have those snakes on the first floor?
一階はまだまだびちょびちょだよ。
The ground floor is still wet.
「荷物はどこに置いたらいいかな？」「一階でも、二階でも、下でも、どこでも。あなたの好きなところに置いてくれていいよ。」「わかったわ。有難う。」
"Where should I put my stuff?" "Here, the first floor, the second floor, anywhere. You can put them any place you’d like." "Okay. Thank you."
The one floor is the first floor (or floor one). Pretty simple.
Unless you're British, that is. For you this is the ground floor!
The reading is on'yomi because it's a jukugo kanji. Be careful of the 一 though. It gets shortened and has a little っ in there.