Create new table row for every 4th loop

<table>
    @for (int i = 0; i < ViewBag.MyItems.Count; i++)
    {
        var cells = 4;
        var item = ViewBag.MyItems[i];

        if ((i % cells) == 0)
        {
            @:<tr>
        }

        <td>
            @item.MyTextOrWhatever
        </td>

        if (i == (ViewBag.MyItems.Count - 1))
        {
            while ((i % cells) != 0)
            {
                @:<td></td>
                i++;
            }
        }

        if ((i % cells) == (cells - 1)) // aka: last row cell
        {
            @:</tr>
        }
    }
</table>

Create Dynamic placeholders to handle multiple components on the same page in sitecore

Dynamic placeholders in Sitecore