I have been inspired by this site for many of my projects. This is one of mine that I would like to share.
When I bought my Honda Civic Hybrid, I lost much of the cargo carrying capacity I had while owning a 95 Geo Metro and 91 Honda Accord. I decided to get a new roof rack but found out that it would cost around $400. While searching the web, I stumbled upon some instructables on homemade roof racks and that gave me the idea for this. Luckily for me I already had an old "BIC" brand (universal) roof rack which I had been using with my 91 Honda Accord but which could not be attached on my civic due to the different roof configuration.
You may be able to find a rack like this cheap on Craigslist or other classifieds site.
I had to remove the old attaching gear and find a way to keep the rack on my civic roof. I used a couple (one for each cross member) of ratchet straps that cost 2 bucks a piece. I did not want to buy expensive straps as this was a trial. Now that I know it works, I will replace these with good quality straps.
Here are the steps.

Tools needed:
Pliers, Drill plus 3/16" drill bit

Parts:
Universal roof rack, 2 Ratchet Tie down Straps

Step 1: Universal Roof Rack

This is a BIC universal roof rack which was given to me by one of my friends several years ago. It used to fit my 91 Honda Accord and several other cars. I have used it with my old cars to carry 2 x 4's, ladders and other stuff. But the system for attaching it to the roof would not work for my new Civic. I removed the existing mounting straps and anchors which hooked above the car doors and replaced that with $2 ratchet straps.
To remove the old hardware, I had to drill out the metal rivets at the strap ends. You can get to these by sliding the rubber protector down off the attaching plate.

Step 2: Drill Out the Rivets

Using a 3/16" drill bit, I drilled 2 rivets from each end and removed them. Make sure to drill the rivet from the "expanded" side not the head.

Step 3: Remove the Hardware From the Strap

Once the rivets are out, the strap can be taken out from the hooking plate. Slide off the rubber protector next.

Step 4: Take Off the Foot and Strap.

There is a rubber pad under each foot which just pops off. You can then see a butterfly nut which can be unscrewed. You may need to use a plier to loosen this if it is too tight. Slide the foot off the bar. Pull out the strap
Repeat Steps 1, 2, 3 & 4 for the other end of the strap.
Follow the same procedure for the other bar.

Step 5: Get the Ratchet Strap Into the Bar.

Insert the end of the ratchet strap through one foot and bar and when it comes out of the other end of the bar, insert it through the other foot and reattach the foot. Tighten the butterfly nuts for the feet and replace the rubber foot covers.

Step 6: Setup on Roof

Place the bar on car roof. Run the straps inside the car with doors open and adjust the position of where the ratchets will hang overhead so that they will not interfere with drivers or passengers' heads. Connect the 2 hooks together and run the free end of the ratchet strap through the winder slot on the ratchet tensioner. Pull it through most of the way before you start working the ratchet. It will automatically wind and tighten the strap.
You may also place pieces of bicycle inner tubing or other suitable material between the straps and the car body where they contact, to prevent scuffing damage to paintwork and door weather stripping. This rack is suitable for carrying 2 x 4's and such. Make sure to tie the load to the crossbars securely. I personally use good quality bungee cords for this purpose. Always drive carefully, checking the load is secure and has not moved after driving a short distance. Avoid driving too fast with roof loads, especially those mounted on homemade racks. I don't need to use the highway when carrying what I need as the big box hardware stores are all near where I live.