How to redirect users to certain page based or username or user role

Step 1:
You need to setup default as intermidiate page. I have called it as Transfer.aspx

<authentication mode="Forms">

  <forms

    loginUrl="~/Login.aspx"

    defaultUrl="~/Transfer.aspx" />

</authentication>

Step 2:
Then please consider setup role based authenticaiton to relevent folders,

  <location path="Admin">

    <system.web>

      <authorization>

        <allow roles="Admin"/>

        <deny users="?"/>

      </authorization>

    </system.web>

  </location>

  <location path="Members">

    <system.web>

      <authorization>

        <allow roles="Member"/>

        <deny users="?"/>

      </authorization>

    </system.web>

  </location>

In the tranfer aspx page.
Point 1:  If you need a just perticular user, to redirect to a certain page, you can simple use user's name.
Transfer.aspx

<%@ Page Language="C#" %>

<script runat="server">

    protected override void OnLoad(EventArgs e)

    {

        if (this.Page.User != null && this.Page.User.Identity.IsAuthenticated)

        {

            if (this.Page.User.Identity.Name.Equals("Admin"))

                this.Response.Redirect("~/Admin/Default.aspx");

            else

                this.Response.Redirect("~/Member/Default.aspx");

        }

        else this.Response.Redirect("~/Login.aspx");

    }

</script>

Point 2:  If you need grop of users (role based) to redirect to a certain page,
Transfer.aspx

<%@ Page Language="C#" %>

<script runat="server">

    protected override void OnLoad(EventArgs e)

    {

        if (this.Page.User != null && this.Page.User.Identity.IsAuthenticated)

        {

            if (this.Page.User.IsInRole("Admin"))

                this.Response.Redirect("~/Admin/Default.aspx");

            else if (this.Page.User.IsInRole("Member"))

                this.Response.Redirect("~/Member/Default.aspx");

            else

                this.Response.Redirect("~/Default.aspx");

        }

        else this.Response.Redirect("~/Login.aspx");

    }

</script>