Some were stones piled together. Some were large metal platforms, others were smaller golden stands. God ordained each of these designs, so we know they were all valid.
Matthew 23:16-22 KJV
16) Woe unto you, ye blind guides, which say, Whosoever shall swear by the temple, it is nothing; but whosoever shall swear by the gold of the temple, he is a debtor!
17) Ye fools and blind: for whether is greater, the gold, or the temple that sanctifieth the gold?
18) And, Whosoever shall swear by the altar, it is nothing; but whosoever sweareth by the gift that is upon it, he is guilty.
19) Ye fools and blind: for whether is greater, the gift, or the altar that sanctifieth the gift?
20) Whoso therefore shall swear by the altar, sweareth by it, and by all things thereon.
21) And whoso shall swear by the temple, sweareth by it, and by him that dwelleth therein.
22) And he that shall swear by heaven, sweareth by the throne of God, and by him that sitteth thereon.
The altar is the place you bring your gift to God, where you dedicate yourself, your things, to Him.
Much love!