Edit in JSFiddle

var oBox = document.getElementById("box");
var aList = oBox.getElementsByTagName("p");
for (var i = 0, len = aList.length; i < len; i += 1) {
    var iCol = 3,
        iNum = i % iCol,
        iMargin = 10;
    aList[i].style.left = (iNum + 1) * iMargin + parseInt(aList[0].offsetWidth * iNum, 10) + "px";

    if (i >= iCol) {
        aList[i].style.top = aList[i - iCol].offsetHeight + aList[i - iCol].offsetTop + iMargin + "px";
    }
}

<div id="box">
    <p class="p3">3</p>
    <p class="p2">2</p>
    <p class="p1">1</p>
    <p class="p2">2</p>
    <p class="p3">3</p>
    <p class="p4">4</p>
    <p class="p3">3</p>
    <p class="p2">2</p>
    <p class="p1">1</p>
    <p class="p2">2</p>
    <p class="p3">3</p>
    <p class="p4">4</p>
</div>

html, body, p {
    margin: 0;
    padding: 0;
}
#box {
    position: relative;
    width: 360px;
    height: 400px;
    background-color: #f2f2f2;
    overflow: auto;
    margin: 0 auto;
}
p {
    position: absolute;
    top: 0;
    left: 0;
    width: 100px;
    background-color: gray;
}
.p1 {
    height: 100px;
}
.p2 {
    height: 125px;
}
.p3 {
    height: 150px;
}
.p4 {
    height: 200px;
}