public function store(Request $request)
     {
         $data =[
           $request->customer_id,
           $request->room_no,
           $request->start_date,
           $request->end_date,
           $request->category,
         ];
       dd($data);
     }

public function up()
        {
        Schema::create('reservations', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->integer('room_no')->unsigned();
            $table->foreign('room_no')->references('room_no')->on('rooms');
            $table->date('start_date');
            $table->date('end_date');
            $table->decimal('amount')->default(0.0);
            $table->bigInteger('customer_id')->unsigned();
            $table->foreign('customer_id')->references('id')->on('customers');
            $table->string('category');
            $table->timestamps();
        });

<form method="POST" action="/reservations/">
        @csrf

        <div>
          <p>
               <b>Enter Reservation for {{$customer->first_name}} {{$customer->last_name}}</b>
           </p>
           <h4 class="info-text">Select Room<br>
            <select name="room_no" id="room_no">
                <option value=100>100</option>
             //...there are more but no need to post ALL of them here
              </select>
           </h4>
            <h4 class="info-text">Select Room Type<br>
             <select name="category" id="category">
               <option value="Deluxe">Deluxe</option>
               // shortened for question's sake again
            </h4>
            <p>
        <b>Enter Start and End Date:</b>
           </p>
           <table>
               <tr>
                   <td>
                     <input class="input" type="date" name="start_date" size="11" />
                     <input class="input" type="date" name="end_date" size="11" />
                   </td>
               </tr>
           </table>
           <b>Cost of Stay</b>
           <td>
             <input class="input" type="decimal" name="amount" size="11"/>
           </td>
        <p><button type="submit">Create Reservation</button></p>
    </div>
  </form>

Route::resource('reservations', 'ReservationsController');
    Route::get('/reservations/create/{customer_id}',
     "ReservationsController@create_reservation");

array:5 [▼
  0 => null
  1 => "106"
  2 => "2019-04-16"
  3 => "2019-04-30"
  4 => "Economy"
]